Democrats, of course, have a reason to issue their warning now: They have a better chance at winning back the Senate seat if Rubio decides to retire at the end of the year. But the DSCC and other Democratic outside groups, including American Bridge and the Senate Majority PAC, are preparing to spend tens of millions in the expensive state against Rubio, and officials say the attacks against the senator in the perennial swing state will be relentless…

John Morgan, an attorney and major Florida Democratic donor, said that Rubio will be “done forever” if he loses a bid for a second term. To make that happen, he said, donors would pour big bucks behind Rep. Patrick Murphy, the favorite of the Democratic establishment, who is facing progressive firebrand Rep. Alan Grayson in the August primary.

“I think if Marco Rubio runs, Patrick Murphy will have more money than he can spend in Florida,” Morgan said.

Rubio has until June 24 to make a decision on whether to run, but the calculation is complicated. Rubio confidantes say he’d like to run for president again, potentially in 2020 if Trump loses this fall, and they believe he could be better positioned to do so by not having the baggage of holding a political office. Yet if the GOP loses his seat, and the Senate majority, Rubio could be accused of not doing more to help his party stay in power. Plus, he could lose a national platform that being a senator provides.