Republican Sens. Jeff FlakeJeffrey (Jeff) Lane FlakeFlake to try to force vote on DACA stopgap plan Congress punts fight over Dreamers to March Outgoing GOP rep: Republican Party 'heading into trouble' in election MORE (Ariz.), Saxby ChamblissClarence (Saxby) Saxby ChamblissLobbying World Former GOP senator: Let Dems engage on healthcare bill OPINION: Left-wing politics will be the demise of the Democratic Party MORE (Ga.), Johnny IsaksonJohn (Johnny) Hardy IsaksonFrustrated Republicans accuse Paul of forcing pointless shutdown Budget deal is brimming with special tax breaks House funding bill includes bipartisan Medicare reforms MORE (Ga.), Dan CoatsDaniel (Dan) Ray CoatsTop state election official questions why Trump is downplaying threat of Russian election interference: report Russian bots turn to gun control after Florida high school shooting: report The case alleging Russian collusion is not closed MORE (Ind.), Chuck GrassleyCharles (Chuck) Ernest GrassleyPavlich: The claim Trump let the mentally ill get guns is a lie Congress fails miserably: For Asian-Americans, immigration proposals are personal attacks Grassley, Dems step up battle over judicial nominees MORE (Iowa), Susan CollinsSusan Margaret CollinsOvernight Tech: Judge blocks AT&T request for DOJ communications | Facebook VP apologizes for tweets about Mueller probe | Tech wants Treasury to fight EU tax proposal Overnight Regulation: Trump to take steps to ban bump stocks | Trump eases rules on insurance sold outside of ObamaCare | FCC to officially rescind net neutrality Thursday | Obama EPA chief: Reg rollback won't stand FCC to officially rescind net neutrality rules on Thursday MORE (Maine), Dean HellerDean Arthur HellerThe siren of Baton Rouge Big Republican missteps needed for Democrats to win in November What to watch for in the Senate immigration votes MORE (Nev.), Kelly AyotteKelly Ann AyotteAudit finds US Defense Department wasted hundreds of millions of taxpayer dollars US sends A-10 squadron to Afghanistan for first time in three years No, the US did not spend million on a gas station in Afghanistan MORE (N.H.), Rob PortmanRobert (Rob) Jones PortmanCommittee chairman aims for House vote on opioid bills by Memorial Day Flake to try to force vote on DACA stopgap plan Congress punts fight over Dreamers to March MORE (Ohio) and Ted CruzRafael (Ted) Edward CruzOvernight Health Care: Trump eases rules on insurance outside ObamaCare | HHS office on religious rights gets 300 complaints in a month | GOP chair eyes opioid bill vote by Memorial Day HHS official put on leave amid probe into social media posts Trump, Pence to address CPAC this week MORE (Texas), as well as Democratic Sen. Martin HeinrichMartin Trevor HeinrichCongress fails miserably: For Asian-Americans, immigration proposals are personal attacks Senate rejects centrist immigration bill after Trump veto threat Dem senators want list of White House officials with interim security clearances MORE (N.M.), are being targeted in the effort.

The ads, which will run on Facebook and on search engines, ask supporters to call the individual senators and express support for expanded gun-control measures.

"Too many Americans are dying from gun violence & Congress needs to act. Call Sen. Collins!" reads the ad running against Collins.

The Senate will begin consideration of a comprehensive gun control bill this week or next; it's still unclear whether President Obama will be able to successfully rally support for one of the most politically feasible measures — universal background checks for gun owners.

Opposition from Republicans and some red-state Democrats has resulted in other Obama priorities, including an assault-weapons ban, being stripped from the main bill.

The passage of universal background checks is largely considered the test of whether Obama's push for expanded gun control measures, which followed the Sandy Hook massacre late last year, has been a success.

The president spent Monday in Hartford, Conn., speaking in support of his effort to reduce gun violence. Vice President Biden and Attorney General Eric HolderEric Himpton HolderPavlich: The claim Trump let the mentally ill get guns is a lie Pennsylvania Supreme Court releases new congressional map 36 people who could challenge Trump in 2020 MORE will address the issue on Tuesday at the White House, and first lady Michelle ObamaMichelle LeVaughn Robinson ObamaMichelle Obama celebrates success of ‘Black Panther’ How textbooks shape teachers — not just their students Michelle Obama dedicates Valentine's Day playlist to Barack Obama MORE will advocate for the package at a speech in Chicago later in the week.

The OFA has been working to support his lobbying effort, issuing ads against 16 GOP lawmakers earlier this year. It hopes the online ad campaigns will pressure some of the 11 senators to support the final bill.

While many of the senators targeted in the new ad push reside in red states where any expansion of gun control measures is unlikely to be politically palatable, some — like Collins and Ayotte — are in states that lean blue and might be open to the bill.

Collins is up for reelection in 2014, and a vote for the gun control bill could give her a boost among Democrats and centrists in Maine.

Chambliss, too, represents a possible GOP vote in favor of a bill, as he's retiring in 2014.

Top aides to the president’s reelection effort relaunched his campaign arm, Obama for America, as the new OFA in January. Now a nonprofit, Organizing for Action can, by law, engage in issue advocacy but not electoral politics. 

It can also receive unlimited donations, and does not have to disclose its donors.

The group has come under fire by campaign finance reform advocates who have expressed concern that special interests can buy “access” to the president through contributions to his advocacy arm, but the group has said it will voluntarily disclose donors.

--This post was updated at 11:33 a.m. on Tuesday.