We already know Senate Republicans really, really want Marco Rubio to run for Senate.

And it looks as if Republican voters in Florida feel the same way. A new poll from the Florida-based Mason-Dixon polling firm finds that almost half of the state's voters — including 77 percent of Republicans — say Rubio should change his mind and run for reelection.

The next key number in this poll helps explain why Republican primary voters are seemingly so enthusiastic about Rubio's running for Senate (even though a majority of them shunned him in the presidential primary): 20 percent. None of the five top candidates currently in the race have hit 20 percent support, according to the Mason-Dixon poll. And almost half of Republican primary voters are undecided:

In other words, Florida's Senate race is wide open, and this poll suggests voters are practically begging Rubio to get in. And the national GOP is probably overjoyed to see this poll; those are pretty irresistible numbers for any politician — even one who's reluctant to run for an office he said he was done with.

When he got into the presidential race, Rubio decided not to run for Senate because (1) Florida law doesn't allow you to be on the ballot twice and because (2) he wanted to open the field for other Republicans to run, including his good friend Lt. Gov. Carlos López-Cantera.

Those decisions have put him in a tough spot. As The Washington Post's Mike DeBonis explains, if Rubio got into the race, he would risk being seen as going back on his word and undermining his friend.

But on the flip side, López-Cantera has yet to distinguish himself in the crowded primary. Nor has any candidate, really. That may explain why Rubio said "maybe" when CNN's Jake Tapper asked in a recent interview whether he would consider running if López-Cantera got out. (Rubio told reporters in Miami this weekend his plans not to run haven't changed — though it's hard not to infer a "yet" in there.)

We recently detailed why top Senate Republicans, including Majority Leader Mitch McConnell (R-Ky.), are pushing their colleague to run. The short version is this: They think he could win. That would keep the seat in Republican hands and could help keep the Senate under Republican control. (Democrats need to pick up four or five seats to take back the Senate, and Florida's open Senate seat is among the more likely to flip.)

If Rubio is having second thoughts about his decision to bow out of politics for now, he's got to decide quickly. The filing deadline is in 18 days and counting.