Sen. Mark PryorMark 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 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 HaganLinking repatriation to job creation Former Sen. Kay Hagan in ICU after being rushed to hospital GOP senator floats retiring over gridlock MORE (D-N.C.) and Mary LandrieuMary LandrieuMedicaid rollback looms for GOP senators in 2020 Five unanswered questions after Trump's upset victory Pavlich: O’Keefe a true journalist MORE (D-La.) all supported the bill. Sen. Al FrankenAl FrankenWhat killing net neutrality means for the internet Overnight Tech: Net neutrality fight descends into trench warfare | Zuckerberg visits Ford factory | Verizon shines light on cyber espionage Franken, top Dems blast FCC over net neutrality proposal 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 KirkThe way forward on the Iran nuclear deal under President Trump ObamaCare repeal bill would defund Planned Parenthood Leaked ObamaCare bill would defund Planned Parenthood MORE (R-Ill.), Kelly AyotteKelly AyotteBottom Line How Gorsuch's confirmation shapes the next Supreme Court battle THE MEMO: Trump set to notch needed win with Gorsuch MORE (R-N.H.) and Dean HellerDean HellerOvernight Energy: Trump orders review of national monuments, claiming ‘egregious abuse’ Draft House bill ignites new Yucca Mountain fight Ex-Nevada state treasurer may challenge Heller in 2018 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 MoranJerry MoranCongress reintroduces IT modernization bill At the table: The importance of advocating for ABLE GOP lawmakers lead way in holding town halls MORE (R-Kans.), as well as both of his NRSC deputies, Sens. Rob PortmanRob PortmanTrump talks big on trade, but workers need action Trump tax plan prompts GOP fears about deficit Overnight Regulation: Senators call for 'cost-effective' regs | FCC chief unveils plans to roll back net neutrality MORE (R-Ohio) and Ted CruzTed CruzTrump’s hands are tied on 9th Circuit Schumer: Trump's handling of North Korea 'all wrong' Net neutrality fight descends into trench warfare 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.