Rubio, meanwhile, was one of the first Tea Party favorites, along with Pat Toomey, the Republican running for Senate in Pennsylvania. Crist has used Rubio's conservative views, particularly that Congress should consider raising the retirement age for Social Security, to try to turn off Florida's retirement population.
Crist has a TV ad accusing Rubio of wanting to raise the retirement age and gut social security.
"Work longer, get by on less, that's the Marco Rubio retirement plan," according to the narrator in Crist's ad. Watch it here.
Compelling Personal Story, Conservative Politics Help Rubio
In addition to hitting Crist as a political opportunist, Rubio has run on his biography, arguing that only in America can the child of refugees from Cuba rise to be a successful lawyer. And it's the American system of free enterprise, according to Rubio, that makes his rise possible.
Rubio's most recent TV ad makes oblique mention of Crist and warns that Washington won't improve "if we keep electing politicians who will say or do anything just to hold office."
But he also has personal financial problems that Democrats and Crist have tried to say make him hypocritical in areas of national fiscal responsibility.
In order to have a chance, according to Smith, Crist, who is closer in polls to Rubio, has to convince Democrats not to vote for Rep. Kendrick Meek, according to Smith.
Democrats Back Meek Even as Crist Pursues Democratic Votes
Meek has attacked Crist in recent TV ads, one of which strings together clips from when Crist was a Republican and praised people like former Florida Gov. Jeb Bush and Alaska Gov. Sarah Palin.
"I'm a pro-life, pro-gun, anti-tax Republican," Crist says at one point in the ad. Watch it here.
Even so, it might be to Democrats benefit in some ways to back Crist. He is perceived as having a better chance to beat Rubio and Democrats could convince him to join their caucus even if he remains technically independent. With the balance of power in Washington in play, that vote could be key.
"Kendrick Meek is our candidate for the United States Senate in Florida," Sen. Bob Menendez, who chairs Democratic Senators' campaign arm, said at an appearance in Washington this week. "And as this race in the next 30-some-odd days, I think will give Kendrick an opportunity to rise significantly in the polls.
"Governor Crist is not doing that well in the polls, and I think when people are looking for a real choice, they will increasingly turn to Kendrick," he said. "So I'm not expecting Gov. Crist coming, I'm expecting Kendrick Meek to come, and he will caucus with the Democrats."
Only Two Independents Currently in Congress
There are currently two independents in Congress, but both, Joe Lieberman of Connecticut and Bernie Sanders of Vermont, side with Democrats in most procedural votes.
Sen. Lisa Murkowski of Alaska lost the Republican primary there to attorney and Tea Party favority Joe Miller. She is mounting a write-in campaign, but has said she would still caucus with Republicans if reelected.
Who Crist would caucus with if he wins has the been a subject of great speculation. He has not said who he would caucus with, but has said he would instead look out for the best interests of the people of Florida. That might sound good to voters, but it would make his vote a hot commodity in the Senate, where the minority party can bring business to a standstill with 41 votes on procedural matters.