(Paul Sancya/AP)

Update: Rubio now tells Politico it's "unlikely" he would change his mind -- a less-definitive statement that he has previously made. The original post follows:

Sen. Marco Rubio (R-Fla.) is getting pressure from Republicans to reverse course and seek reelection to the Senate, CNN's Manu Raju reported Thursday. But he's also been pretty clear that he won't do it, and there are plenty of reasons to believe him.

Rubio's position as a Washington insider, his declining popularity in Florida, the fact his friend is already in the race, the fact that the filing deadline is a month away and the fact that he'd be starting an expensive statewide campaign with just five months to go are all really solid reasons for a guy who reportedly really dislikes the Senate to say no.

"It's not that he dislikes the Senate, it's that the decision has been made and there's really no reason to revisit it," said a source familiar with Rubio's thinking.

But it's just as easy to see why Florida and national Republicans want him to say yes. Florida is ranked third on our list of 10 Senate seats most likely to flip parties this November. That's in part because the state tends to be a little bluer in a presidential year. But it's also because, of the five or so top Republican candidates, not one has managed to pull ahead as the favorite ahead of the Aug. 30 primary.

Rubio, the (wishful) thinking goes, could make Republicans' name ID and fundraising problems go away almost instantly. (Rubio decided to leave the seat and run for president, since Florida law doesn't allow him to do both at the same time. In addition, Florida's swing state status made it harder for Rubio to do what Rand Paul did and simply fall back on running for reelection.) And that's a big deal, given which party wins Florida, the thinking goes, will probably win the Senate.

"If you're a conservative and want to make a difference, the number one thing you can do is win the White House," said Josh Holmes, a former chief of staff to Senate Majority Leader Mitch McConnell (R-Ky.). "The number two thing is probably this."

Conservative consultant circles are flush with polls showing Rubio beats the two Democratic candidates in the race, Reps. Patrick Murphy and Alan Grayson, by a long shot. Which is why they're pushing pretty hard to keep him in, Holmes said. If Rubio runs for reelection, Senate Republicans don't have to pour millions and millions into a competitive race to try to keep the state red.

"If you can take that off the table with one candidate, you do it," Holmes said.

Plus, some pretty influential GOP senators like Rubio and his foreign policy chops:

But that is indeed wishful thinking. There's very little evidence that reelection would be a smooth ride for Rubio, and plenty of evidence to the contrary.

Speaking to reporters Thursday, CNN reported Rubio said it was "unlikely" he'll run for Senate. His spokesperson, Alex Burgos, said Rubio has "repeatedly ruled that out."

Here's just one number we'll highlight that could explain why: 27 percent. That's how much of the vote Rubio got in his home state primary in March. The only county out of 67 he won was his own, Miami-Dade. Donald Trump got 46 percent of the vote and won the state.

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In other words, Rubio's stock back home doesn't seem to be particularly strong right now, which means there is no guarantee that a last-minute change of course would bear fruit. He was counting on Florida to save his presidential hopes, and Florida turned its back on him.

Indeed, Rubio's image back home was somewhat eroded during his presidential run, suggesting that he'd have to start out his Senate campaign doing damage control. A recent Quinnipiac poll pegged his approval rating at 42 percent, with 49 percent disapproving. And remember how one of Florida's largest newspapers, the Sun-Sentinel, demanded that he resign in light of an October Washington Post report that he perhaps hated -- or at least was frustrated by -- the Senate?

"If you hate your job, senator, follow the honorable lead of House Speaker John Boehner and resign it," the editorial read.

Rubio spent the rest of the campaign trying to defend his spotty Senate attendance record. Yes, his gifted debate skills helped him do that somewhat successfully -- remember the time he owned his former mentor, Jeb Bush, when Bush tried to bring that up?

But Rubio wasn't exactly perfect. When he did malfunction on the national stage, it was spectacular and it often stuck. Remember the robotic debate performance that possibly sealed the fact that he wasn't going to win?

Those could all be things that would be fresh in voters' minds if he suddenly stood on a podium in front of them asking for their votes.

But let's say, for argument's sake, that Rubio does change his mind about the Senate and decides to get into the race -- something he told CNN pretty flatly that he wouldn't do. There are several big hurdles he'd have to overcome right away.

Now that he's off the presidential ballot, Rubio could simply announce he's running for reelection, file the paperwork by the June 24 deadline and rev up his Senate campaign, which does have $3.3 million in the bank.

But in an expensive and big media market like Florida, he would want to raise many millions more -- and quickly.

He'd also first face an awkward situation with his "really good friend" Carlos Lopez-Cantera, the state's lieutenant governor and the guy Rubio has indicated recently he'd be endorsing in the Senate race. Stepping aside for a friend to run and then jumping back in at the last moment is a recipe for very hard feelings, especially as Lopez-Cantera appears to have a good shot at the GOP nomination.

"He's not going to do that to his friend," the source familiar with Rubio's thinking said.

Let's say, once again for argument's sake, Rubio does all of that. He runs against or pushes out his buddy, and the state's big GOP donors who had been holding their cash in the primary start writing big checks to him. He's the front-runner.

But if he doesn't clear the field, it's easy to see how his top primary opponents would hold their fire on each other and cast Rubio as an opportunistic, career politician -- in a cycle where that's not really the kind of candidate voters seem to be going for. Rubio's own words would be right in front of him for them to use: "I’m not running for reelection to the Senate," he said March 17.

Finally, Rubio just seems like a guy who doesn't want it right now. The presidential campaign didn't go as planned, and he's pretty clearly looking forward to the cash and freedom that the private sector would provide for his family and three young children.

Upon his return to the Senate this spring, he told reporters that he doesn't want to be vice president, that he doesn't want to run for governor and he even apparently smiled when he said, "I'll be a private citizen in January."

Sure, saying "no" to the veep speculation is perhaps par for the course for wannabee veeps, but Rubio's "no" just seems different and firmer. Rubio seems like a guy who put his all into a political race, lost and is now ready for something entirely different.

What might that be? It's possible not even he knows. But there are all kinds of reasons he won't give in to pressure to attempt a return to the Senate this year.