Florida Sen. Marco Rubio was a darling of the Republican establishment heading into the 2016 presidential election. His campaign even served as a rallying point for mainstream GOP backers after former Florida Gov. Jeb Bush dropped out of the race.

But Rubio’s entire political future is now at stake — and close aides are reportedly begging him to suspend his presidential campaign.

At issue is the upcoming March 15 primary in Rubio’s home state of Florida. Polls show Rubio is going to lose to billionaire Donald Trump, and failure to carry his home state could doom Rubio’s political future in Florida.

And, as first reported by CNN, aides are trying hard to make the case to Rubio that he should drop out before the primary.

“He doesn’t want to get killed in his home state,” one source told CNN, warning Rubio that “a poor showing would be a risk and hurt his political future.”

Others are pointing to today’s primaries as the last straws for Rubio. He is projected to perform especially poorly at the ballot box in Michigan.

“Not going to have a great day is an understatement,” one campaign adviser said.

It’s not just advisers backing away from the Rubio campaign. Just when he needs them the most, big-dollar contributors from the party’s wealthy mainstream are having second thoughts about Rubio’s future.

“Super Tuesday came and Rubio didn’t do as well as some of us hoped. So people are saying, ‘Let’s see how this thing shakes out,'” said Craig Duchossois, who contributed $500,000 last year to a group that backed former Florida Gov. Jeb Bush.

“I’m holding back,” the Chicago-based investor said of his own plans.

Even Rubio’s most bullish aides concede he likely cannot remain in the race without winning in Florida, where public polls show him second to Trump.

The must-win scenario is a result of Rubio’s struggle to find a reliable base in the splintering Republican electorate.

He’s largely failed to reconnect with the Tea Party voters who made him a favorite during their national breakthrough six years ago, instead watching them flock to presidential rivals Trump and Texas Sen. Ted Cruz.

Rubio also has not fully harnessed the financial muscle of the GOP old-guard eager to derail Trump, despite the shift in focus by many to Rubio after Bush quit the race last month.

Rubio had about $5 million in available cash at the beginning of last month, less than half of what Cruz had on hand. Trump has said he can afford to finance his own campaign, though he has received contributions.

Rubio noted Monday how “expensive” it is to campaign in Florida, which he said is “like running in four or five different states” given the many large television markets. Already Monday, Trump had launched a 60-second ad casting Rubio’s as dishonest.

Duchossois and others who pinned their hopes to him said they were turned off by Rubio’s taunts, including calling Trump’s “the worst spray tan in America” and equating Trump’s disproportionately small hands with his manhood.

“You just don’t do that,” said Bill Kunkler, another Chicago Republican who backed Bush but stopped short of the pivot to Rubio. “In Rubio, I don’t see the presidential gravitas.”

The Associated Press contributed to this article.