Five possible successors to Mattis

President TrumpDonald John TrumpLiz Cheney: 'Send her back' chant 'inappropriate' but not about race, gender Booker: Trump is 'worse than a racist' Top Democrat insists country hasn't moved on from Mueller MORE may find it difficult to replace Defense Secretary James MattisJames Norman MattisWatchdog: Former Pentagon spokeswoman misused staff for personal errands Senate panel advances Pentagon chief, Joint Chiefs chairman nominees The Hill's Morning Report - A raucous debate on race ends with Trump admonishment MORE following the Pentagon chief’s resignation this past week.

Mattis, who resigned Thursday after major policy disagreements with his commander in chief, enjoyed broad bipartisan support and the respect of U.S. allies, and for almost two years was able to weather a chaotic administration that has seen an unprecedented amount of Cabinet turnover.

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As Trump now looks to replace the former four-star general by the end of February, several names have emerged as possible front-runners.

But with few prospects who see eye to eye with the president and could garner sufficient support in the Senate, Trump’s top choice is anyone’s guess at this point.

“You got to find people who are willing to do it, and I think a lot of people are upset with [the Syria] call and also the second call where he’s talking about downgrading the Afghan numbers,” Senate Armed Services Committee Chairman James InhofeJames (Jim) Mountain InhofeSenate panel advances Pentagon chief, Joint Chiefs chairman nominees Trump's pick to lead Pentagon glides through confirmation hearing Trump says US will not sell Turkey F-35s after Russian missile defense system purchase MORE (R-Okla.) said, referring to Trump’s decision to withdraw U.S. troops from Syria and his consideration of halving the number of troops in Afghanistan.

Here are five potential candidates to succeed Mattis:

Former Sen. Kelly AyotteKelly Ann AyotteKey endorsements: A who's who in early states Sinema, Gallagher fastest lawmakers in charity race New Hampshire senator to ask 2020 Dems to back repeal of state residency law MORE (R-N.H.)

Sources close to the administration mentioned Ayotte as a possible Mattis successor. She was among those considered for the position before Mattis was nominated for the post.

The former New Hampshire senator has a strong defense background, having served as chairwoman of the Senate Armed Services readiness subcommittee while in Congress.

She lost her reelection bid in 2016, but before that was an outspoken GOP opponent of the 2015 Iran nuclear deal. She has also called for tighter sanctions on Iran and North Korea.

Not long after leaving the Senate, Ayotte served as the sherpa on Capitol Hill for Trump’s first Supreme Court nominee, Neil Gorsuch. Her name was also mentioned for other administration posts, including FBI director after Trump fired James ComeyJames Brien Comey10 questions for Robert Mueller Comey pens blog revealing what he would ask Mueller in upcoming testimony FBI's spreadsheet puts a stake through the heart of Steele's dossier MORE in May 2017.

But some of Ayotte’s positions may put her at odds with Trump, including her views on a troop pullout in the Middle East.

Ayotte criticized former President Obama for withdrawing U.S. troops from Iraq in 2011, indicating she may feel the same about Trump’s desired troop pullout in Syria.

While in the Senate, she was known as one of the “three amigos” with the late Sen. John McCainJohn Sidney McCainMichelle Obama weighs in on Trump, 'Squad' feud: 'Not my America or your America. It's our America' Meghan McCain shares story of miscarriage Media cried wolf: Calling every Republican a racist lost its bite MORE (R-Ariz.), a frequent Trump antagonist, and Sen. Lindsey GrahamLindsey Olin GrahamDemocrats should rise above and unify against Trump's tweets US-Saudi Arabia policy needs a dose of 'realpolitik' Media cried wolf: Calling every Republican a racist lost its bite MORE (R-S.C.), who has been sparring with Trump in recent days over Syria and Afghanistan but is otherwise a strong ally of the president.

Sen. Tom CottonThomas (Tom) Bryant CottonLawmakers introduce bill to block U.S. companies from doing business with Huawei Five things to know about Iran's breaches of the nuclear deal Hillicon Valley: Trump gets pushback after reversing course on Huawei | China installing surveillance apps on visitors' phones | Internet provider Cloudflare suffers outage | Consumer groups look to stop Facebook cryptocurrency MORE (R-Ark.)

Speculation has circulated for months that Cotton — a member of the Senate Armed Services and Intelligence committees — could be tapped for a top role at the Defense Department or the CIA.

Cotton did not respond to reporters who tried to ask him about the opening on Friday.

As a former Army officer and veteran of the Iraq and Afghanistan wars, Cotton has made a name for himself in the Senate as a combative defense hawk. He has also backed Trump on major policy moves against Iran.

But at 41 years old he would be one of the youngest Cabinet picks in recent memory.

He’s also had some missteps. It was Cotton who reportedly suggested H.R. McMaster to Trump as national security adviser after Michael Flynn resigned in February 2017.

McMaster, who reportedly was not on the president’s radar until Cotton’s suggestion, ultimately butted heads with Trump and his approach to Russia, Iran and North Korea and was dismissed in March.

Cotton also broke with Trump on the announcement of plans for drawdowns of U.S. forces in Syria and Afghanistan, issues that also led to Mattis’s resignation.

Andy Keiser, a principal at the lobbying firm Navigators Global who worked on the Trump transition team's national security section, said he was unsure what effect Cotton’s position on Syria would have on his chances for defense secretary.

“That’s a really hard one to gauge,” he said. “Nikki HaleyNimrata (Nikki) HaleyAmerican women can have it all State denies report ex-spokeswoman received Fox salary while in administration Trump rules out Haley joining 2020 ticket MORE was pretty critical of the president and she got [U.S. ambassador to the United Nations]. So hard to judge what importance they place on one comment or another. Being fair, I think Tom Cotton is seen pretty favorably inside the White House and has spoken quite favorably of the president 99 percent of the time. So I think he would be on the safe side of that ledger.”

But complicating matters is whether Cotton would leave a safe Senate seat for a Cabinet position, and whether Trump would draw from the Senate.

Former Treasury Department official David McCormick

McCormick was named as a possible Mattis replacement by The Washington Post in September, when speculation of a post-midterm Mattis departure first sprang up.

A West Point graduate, McCormick is a combat veteran of the first Gulf War. During the George W. Bush administration, he served as under Treasury secretary for international affairs after stints as under secretary of Commerce for industry and security and deputy national security adviser for international economic policy.

He is now co-CEO of the world’s largest hedge fund, Bridgewater Associates, and is engaged to Dina Powell, Trump’s former deputy national security adviser for strategy.

He is said to run in the same social circles as Ivanka TrumpIvana (Ivanka) Marie TrumpTrump steps up attacks on 'Squad' after post-rally furor Trump says he doesn't care if attacks on 'Squad' hurt him politically EXCLUSIVE: Career officials rebut claims of White House interference in security clearance process MORE and Jared KushnerJared Corey KushnerTrump talks to Swedish leader about rapper A$AP Rocky, offers to vouch for his bail Trump: 'We already started' talks to get A$AP Rocky home from Sweden Kim Kardashian West thanks Trump, Kushner for helping efforts to free A$AP Rocky from Swedish jail MORE, the president’s daughter and son-in-law, who both serve as senior White House advisers.

In 2017, though, he reportedly turned down an offer to be deputy Defense secretary because he was happy at his job at Bridgewater and did not feel that role was the right fit for him.

Deputy Defense Secretary Patrick Shanahan

Trump has settled on deputies before when he couldn’t find a replacement for a Cabinet head, and that could work to former Boeing executive Patrick Shanahan’s advantage.

The Pentagon’s second-highest-ranking civilian has an extensive corporate background, having started at Boeing in 1986, and was the senior vice president of the company’s supply chain and operations before he was tapped for the administration post in early 2017.

What’s more, Shanahan has taken on the role of reforming the Pentagon in its business and administrative practices rather than focusing or advising on war-fighting policy.

Shanahan has not only backed up Trump’s plans for a separate Space Force military service, he also leads the project within the Pentagon, frequently visiting the president and Vice President Pence at the White House.

He was not known to be close with Mattis.

Former Sen. Jim Talent (R-Mo.)

Shortly after the 2016 election, Trump’s transition team made a push for Talent to serve as Pentagon chief. The former Missouri senator, who previously served on the Armed Services Committee and maintains strong ties to Capitol Hill, even met with Trump in New York. And unlike many other Republicans in 2015 and 2016, he did not criticize Trump during the campaign

While in the running for Defense secretary, Talent was pushed largely by then-incoming White House chief of staff Reince PriebusReinhold (Reince) Richard PriebusTrump's no racist — he's an equal opportunity offender Press: Acosta, latest to walk the plank Author: Paul Ryan saw retirement as an 'escape hatch' from Trump MORE. But Priebus left the White House in July 2017, and it’s unclear if Talent has an influential West Wing supporter in his corner this time around.

Talent currently serves on the U.S.-China Economic and Security Review Commission, and he was appointed to the position by Senate Majority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellMcConnell challenger faces tougher path after rocky launch Funding a strong defense of our nation's democratic process can't wait The Hill's Morning Report: Trump walks back from 'send her back' chants MORE (R-Ky.) for a two-year term that expires at the end of 2019.

James Carafano, a defense policy analyst at the Heritage Foundation who served on Trump’s transition team, mentioned Talent, as well as Sen. Jon Kyl (R-Ariz.), when asked who he thinks would make a good replacement.

“Somebody like a Jon Kyl or a Jim Talent — an experienced, respected senator that has real chops in terms of knowing national security issues, that people really respect that have been in the trenches in the Congress — somebody like that would be great,” he said. 

Talent was GOP presidential nominee Mitt RomneyWillard (Mitt) Mitt RomneyDemocrats should rise above and unify against Trump's tweets Trump steps up attacks on 'Squad' after post-rally furor Media cried wolf: Calling every Republican a racist lost its bite MORE’s top pick for Defense secretary in 2012.