Sen. Mark PryorMark Lunsford PryorMedicaid rollback looms for GOP senators in 2020 Cotton pitches anti-Democrat message to SC delegation Ex-Sen. Kay Hagan joins lobby firm MORE (Ark.) and other vulnerable Senate Democrats up for reelection this year voted yes in a key test vote Monday on immigration reform.

Every Democrat present voted to advance a border security measure that was added to the underlying Senate bill.

Beesides Pryor, Sens. Mark BegichMark Peter BegichPerez creates advisory team for DNC transition The future of the Arctic 2016’s battle for the Senate: A shifting map MORE (D-Alaska), Kay HaganKay Ruthven Hagan2020 Dems compete for top campaign operatives Senate GOP rejects Trump’s call to go big on gun legislation Politics is purple in North Carolina MORE (D-N.C.) and Mary LandrieuMary Loretta LandrieuSenate GOP rejects Trump’s call to go big on gun legislation Project Veritas at risk of losing fundraising license in New York, AG warns You want to recall John McCain? Good luck, it will be impossible MORE (D-La.) all supported the bill. Sen. Al FrankenAlan (Al) Stuart FrankenFranken to make first public appearance since resignation Overnight Cybersecurity: Fallout from Comey memos | IG reportedly investigating memos over classified info | DNC sues Russia, Trump campaign | GOP chair blasts FDIC over data security Why Smokin' Joe leads the pack of 2020 Democratic hopefuls MORE (D-Minn.), who is seen as less vulnerable, also voted yes.

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So did Sen. Brian Schatz (D-Hawaii), who's likely to face a tough primary against Rep. Colleen Hanabusa (D-Hawaii).

A number of swing- and blue-state Republicans who could face tough reelection battles in future years joined them

Sens. Mark KirkMark Steven KirkHigh stakes as Trump heads to Hill Five things to watch for at Trump-Senate GOP meeting Giffords, Scalise highlight party differences on guns MORE (R-Ill.), 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 (R-N.H.) and Dean HellerDean Arthur HellerSenate GOP wary of new tax cut sequel GOP Senate hopefuls race to catch up with Dems Family, friends mourn death of Barbara Bush MORE (R-Nev.) were among the 15 Republican yes votes. Kirk and Ayotte are up for reelection in 2016, while Heller won't face the voters until 2018.

Some notable opponents: National Republican Senatorial Committee Chairman Jerry MoranGerald (Jerry) MoranOvernight Health Care: Teen pregnancy program to focus on abstinence | Insurers warn against short-term health plan proposal | Trump VA pick faces tough sell Trump VA pick faces challenge to convince senators he’s ready for job Overnight Finance: Senate repeals auto-lending guidance, shattering precedent with vote | House passes IRS reform bills | Senate GOP fears tax cut sequel MORE (R-Kans.), as well as both of his NRSC deputies, Sens. Rob PortmanRobert (Rob) Jones PortmanTax rules will be subject to more OMB review under new memo Ending sex trafficking tomorrow requires preventing child abuse today Doctors bristle at push for opioid prescription limits MORE (R-Ohio) and Ted CruzRafael (Ted) Edward CruzAfter Dems stood against Pompeo, Senate’s confirmation process needs a revamp Cruz's Dem challenger slams Time piece praising Trump Race for Republican Speaker rare chance to unify party for election MORE (R-Texas).

Cruz has been a strident opponent of the bill, but Portman was viewed as a gettable vote for the amendment's advocates. Sen. Pat Toomey (R-Pa.), who's likely to face a tough race in 2016, also voted against the amendment.

It’s unclear whether some of those who voted yes on Monday will vote no in a final vote later this week.

It’s also possible that some Republicans who voted no on Monday could reverse themselves later in the week. Voting no on Monday could allow some senators to retain leverage. Portman, for example, is pushing for language on immigration enforcement to be added to the bill.