Washington (CNN)The two Senate Republicans in the most jeopardy of losing their seats in 2018 faced a choice in Tuesday's health care vote: Stick with President Donald Trump and face a barrage of Democratic attacks, or break ranks and risk a potentially serious primary challenge fueled by Trump himself.
Both Nevada Sen. Dean Heller and Arizona Sen. Jeff Flake decided to stick with Trump.
Their votes came after stern signals from the White House that the President was willing to work to defeat his own party's incumbents if they crossed him on health care.
Trump and White House aides have met and spoken with several potential Flake primary challengers.
And Trump, sitting next to Heller at a recent meeting, predicted the Nevada senator would reverse himself and vote to advance the GOP's health care effort Tuesday.
"He wants to remain a senator, doesn't he?" Trump said.
Conservative Kelli Ward is already challenging Flake in the primary, and former Arizona state GOP chairman Robert Graham told CNN either he or state treasurer Jeff DeWit could also enter the race. In Nevada, Danny Tarkanian -- the son of legendary UNLV basketball coach Jerry Tarkanian -- told CNN he is considering challenging Heller in the GOP primary.
Democratic Rep. Jacky Rosen is running for Heller's seat in Nevada, while several Democrats in Arizona are still weighing potential runs.
Both Flake and Heller gambled that their votes Tuesday could assuage their party's base -- and that, if the chaotic process the Senate is entering doesn't result in the passage of a major Obamacare repeal bill, the political impact next November would be muted.
Still, as soon as they'd voted, Democrats began attacking the two -- with Heller in particular facing questions about why he'd reversed the stance he'd taken weeks ago.
Already, the Democratic Senatorial Campaign Committee had launched radio ads Tuesday accusing Heller and Flake of "dismantling our health care."
After the vote, the DSCC lambasted Heller for casting the "deciding vote" -- a label that could be applied to any Republican, since the party voted to advance the bill in the Senate without any votes to spare.
The Democratic super PAC Priorities USA also launched a digital ad campaign hitting Republicans in seven states -- Heller's Nevada and Flake's Arizona, as well as five others where Democratic senators are up for re-election.
For Heller, in particular, Tuesday's vote raised questions about why he'd stood with popular Republican Gov. Brian Sandoval and said he'd oppose the bill just weeks ago.
"Obamacare isn't the answer, but doing nothing to try to solve the problems it has created isn't the answer either. That is why I will vote to move forward and give us a chance to address the unworkable aspects of the law that have left many Nevadans -- particularly those living in rural areas -- with dwindling or no choices," Heller said in a statement.
He added that he plans to support efforts to "protect Nevadans who depend on Medicaid" -- a reference to the 210,000 who gained coverage under Obamacare's Medicaid expansion, who he'd recently cited as the reason he would oppose an earlier Senate Republican health care bill.
"If the final product isn't improved for the state of Nevada, then I will not vote for it; if it is improved, I will support it," Heller said.