Five reasons Marco Rubio might not enter the race for president in 2016

Sen. Marco RubioMarco Antonio RubioWhite House makes push for paid family leave and child care reform Tom Hanks weighs in on primary: 'Anybody can become president' GOP senator blocks bill aimed at preventing Russia election meddling MORE (R-Fla.) has been everywhere the last few weeks, leads in early polls of the 2016 GOP field, and conventional wisdom is that he's a lock to run for president. But here are five reasons why he might not enter the race.

1. Immigration

Rubio has leaned hard into the bipartisan push for immigration reform, closely associating his name with the effort and staking a good chunk of his reputation on its success. That’s a major switch from late last year, when he seemed more resistant to embracing such a prominent role on the issue.

Rubio has become the bipartisan Senate proposal’s chief spokesman to his party's conservative base, a risky position to take.

While many conservative leaders have so far praised his efforts — or at least held their tongues and awaited judgment until the senators produce a bill — it was unclear when Rubio took on that role whether his popularity with conservatives would be enough to temper their concerns. His decision to forge ahead anyway showed he was willing to out on a limb a bit on the policy even if it could hurt potential presidential aspirations.

So far, criticism on the right has been much more muted than it was the last time bipartisan efforts at immigration reform were attempted, partly due to the base's reverence for Rubio. And successful legislation could bolster his reputation both with primary voters and the electorate in general. But if the GOP grassroots turns hard against the bill, there is a risk that Rubio could feel some of their backlash.

2. Jeb Bush

Rubio and former Florida Gov. Jeb Bush (R) are close — Rubio was a Bush disciple in Florida, they share a number of key advisors, and they remain on good terms personally.

Most Republicans close to both expect they won't run against one another, and Bush has sounded more open to running for president than in previous years — he has a book coming out on immigration and a public tour as well, a sign he's seeking center stage for the first time since he left the governor's mansion more than six years ago.

Bush and Rubio also are focused on many of the same issues, immigration and education chief among them. While the two hold very similar views on education, Bush has been willing to go further on immigration issues than Rubio and has been more vocal in criticizing his own party, which could trip up Rubio if he gets too closely tied to Bush’s position.

3. Family

Rubio has four young kids ranging in age from 12 to 7, and often discusses the guilt he feels at having to spend so much time away from them — much more than many other politicians.

If he runs for president, Rubio's already-busy schedule will take him away from his family even more often. He's shown he's focused on spending as much time with them as possible — he's moving them up to Washington, D.C., and has continued to coach his son's football team — and a presidential bid would mean weeks and months of constant travel away from them, working the small towns of the early voting states.

"You only get that big plane at the end," Rubio said last week at an event hosted by Buzzfeed, when talking about his thoughts on a potential run. "The beginning of it, you're in a rent-a-car in Iowa, and New Hampshire, and South Carolina, you're meeting the same ten people over and over again and they're still undecided."

4. Money

Rubio, unlike many other U.S. senators, is not a very wealthy man. He until recently was still paying off student loans, and his Florida homes had underwater mortgages, according to the most recent personal financial disclosures. He's likely improved his standing since then — his book debuted on The New York Times best-seller list and has sold well — but he has nowhere near the money many other politicians do.

Rubio has quickly become a huge star in the party, and if he decided to go to the private sector instead of running for president he could easily make millions by joining corporate boards, giving speaking tours and possibly anchoring a television show. Running for president would forestall that for a while.

5. The field

While Rubio has led in all early polls of the potential 2016 field, there are a number of other strong candidates considering bids, many of whom took a pass on running in 2012. While that might not be a deterrent, it's highly unlikely he'd be able to cruise to the nomination.

An even bigger question is whether Hillary ClintonHillary Diane Rodham ClintonNo, the polls aren't wrong — but you have to know what to look for How to shut down fake Republican outrage over 'spying' on Trump More than 200,000 Wisconsin voters will be removed from the rolls MORE runs. Clinton could clear the Democratic field and while her astronomical current standing in the polls is likely to come down, she presents a formidable obstacle, especially for a candidate like Rubio who is young enough to wait for another opportunity.

Clinton led Rubio in a recent national poll from Democratic-affiliated Public Policy Polling (PPP) by a large 49 to 41 percent, and has led in PPP polls over Rubio in such red states as Texas and Kentucky. He's a very popular politician, but it may be smart not to take her on if she remains anywhere near as popular in a few years as she is currently.