9 GOP senators Trump must watch out for
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The fate of President Donald Trump's legislative agenda will be determined in the Senate.

Even though Republicans control the body, their 52-seat majority is thin and can't stand many desertions. Each Republican senator is critically important. It will only take a few of them to stop the Trump train on any given issue.

The Senate's 60-vote majority is always a stumbling block on matters where filibusters can be used. Even on issues where it only takes a simple majority to get things done in the Senate — such as confirming presidential appointments (other than the Supreme Court) and passing reconciliation legislation — getting the needed 51 votes may, in some instances, be difficult.

With this in mind, it’s worth watching nine Republican senators who, for one reason or another, could play a big role — including that of adversary — on key parts of the new White House agenda.

The most prominent GOP senator who spells trouble for Trump is John McCainJohn Sidney McCainEx-McSally aide pleads guilty to stealing over 0K in campaign funds DOJ: Arizona recount could violate civil rights laws Cheney fight stokes cries of GOP double standard for women MORE. The former presidential nominee gets loads of media coverage, especially when he bucks his own party. A former prisoner of war in Vietnam, he will never forget Trump's criticism of his military service ("I like people who weren't captured.") The irascible Arizona senator is already on the warpath, focused on U.S. relations with Russia and the hacking issue.

Another thorn in Trump's side is Lindsey GrahamLindsey Olin GrahamLindsey Graham: GOP can't 'move forward without President Trump' House to advance appropriations bills in June, July The unflappable Liz Cheney: Why Trump Republicans have struggled to crush her  MORE of South Carolina. He ran against Trump for the GOP nomination and said some rough things on the campaign trail. Graham and McCain are working in tandem — as they usually do — to box in Trump on national security issues.


The third senator to watch is Rand PaulRandal (Rand) Howard PaulTim Scott sparks buzz in crowded field of White House hopefuls Sherrod Brown calls Rand Paul 'kind of a lunatic' for not wearing mask Overnight Health Care: WHO-backed Covax gets a boost from Moderna MORE, also a Trump rival in last year's presidential primaries. The two wrangled throughout the presidential debates, and Trump even made fun of the Kentucky senator's appearance. Paul is already questioning Trump's approach on healthcare reform and its impact on the federal deficit.

Then there is Susan CollinsSusan Margaret CollinsCheney drama exposes GOP's Trump rifts House to advance appropriations bills in June, July Manchin touts rating as 'most bipartisan senator' MORE of Maine, perhaps the least conservative Republican in the Senate. She's remembered for her famous "I will not be voting for Donald Trump" statement after he became her party's presidential nominee.

Next is Marco RubioMarco Antonio RubioDemocrats cool on Crist's latest bid for Florida governor Tim Scott sparks buzz in crowded field of White House hopefuls The unflappable Liz Cheney: Why Trump Republicans have struggled to crush her  MORE, who famously squared off against the New York billionaire during their nasty GOP nomination brawl. The Florida senator, who still harbors higher ambitions, may want to keep a respectable distance from his former nemesis on some issues. His tough questioning of Secretary of State nominee Rex Tillerson was an early example.

There is also Jeff FlakeJeffrey (Jeff) Lane FlakeThe unflappable Liz Cheney: Why Trump Republicans have struggled to crush her  Cindy McCain: Arizona election audit is 'ludicrous' The Republicans' deep dive into nativism MORE of Arizona, an independent-minded reformer and Trump critic; Ben Sasse of Nebraska, a leader in last year's Never Trump movement; Lisa MurkowskiLisa Ann MurkowskiPollster Frank Luntz: 'I would bet on' Trump being 2024 GOP nominee Trump muddles Republican messaging on Afghanistan Trump drama divides GOP, muddling message MORE of Alaska, who called on Trump to resign as presidential nominee after the "Access Hollywood" video surfaced; and Lamar AlexanderLamar AlexanderThe Republicans' deep dive into nativism Senate GOP faces retirement brain drain The Hill's Morning Report - Presented by the National Shooting Sports Foundation - CDC news on gatherings a step toward normality MORE — a former governor of Tennessee, U.S. Education secretary and presidential candidate — who has tussled with Trump over the years.

Of course, Republicans in Congress who too often oppose their president must be prepared to hear from his supporters back home and maybe even risk a primary challenge in the next election. Flake already has a Trump backer running against him in the 2018 GOP primary.

For sure, Trump will have his hands full fighting off Democrats. They've already set up a war room to oppose him. But, the new president will also have to look over his shoulder at some of his fellow Republicans.

Yes, Trump is captain of the ship — but it will never leave the dock unless most of the Gang of Nine are on board.

Ron Faucheux, Ph.D., is a political analyst, author and pollster. He publishes LunchtimePolitics.com, a daily newsletter on polls. He also runs Clarus Research Group, a nonpartisan survey research firm.

The views expressed by contributors are their own and not the views of The Hill.