They may soon be rewarded.
After tens of millions of dollars have poured into the race, some political scientists said in interviews Wednesday that Rubio could have the edge over Democratic challenger Patrick Murphy —- though the Senate battle also has links to the presidential campaign in Florida between Republican Donald Trump and Democrat Hillary Clinton.
"A Rubio win in my mind is expected," said Michael Binder, director of the University of North Florida's Public Opinion Research Lab. "A Trump win in Florida would surprise me, but as the Dems fail to take the lead in the early votes my expectations (are) shifting."
It's not a fait accompli for Rubio in a race that could help determine which party controls the Senate in 2017 and 2018. But experts say the path appears smoother for Rubio than Murphy, a congressman from Jupiter.
University of South Florida political science professor Susan MacManus said Murphy, who has struggled for recognition throughout the campaign, may require strong "pantsuit tails" from Clinton for a win at this point.
"Murphy is more tied to Hillary than Rubio to Trump," MacManus said. "In some ways, the die is cast for each of them by the turnout."
More than one-third of Florida's 12.86 million registered voters had already cast ballots as of Thursday morning. Of the votes cast through early voting and vote-by-mail, 40.03 percent have been made by registered Republicans and 39.78 percent by Democrats.
But MacManus added that a large unknown remains independents, as most of the focus has been on analyzing the numbers of registered Republicans and Democrats who have already voted.
"Really, I don't think we have a good feel, from the polls I'm looking at," MacManus said. "Everyone is making all these speculations, but we're leaving out one-fourth of the equation."
Still, Aubrey Jewett, a political science professor at the University of Central Florida, noted that as Trump appears to have closed the margin or surpassed Clinton in the presidential race in Florida, it isn't as likely that Murphy will benefit from a strong Democratic wave.
"I don't think that there is much that Rubio or Murphy can do at this point to change the dynamics of the race," Jewett said. "Of course, if one of the candidates does something really outrageous or stupid or if something is released that is incredibly embarrassing or unethical about one of the candidates, then the race could still change. This is Florida after all, and we have seen our share of election surprises over the years."
A Quinnipiac University poll released Thursday showed Rubio with a six-point lead, though a CNN/ORC International poll released Wednesday had him up by 1 percentage point. Other polls released during the past week have showed varying results.
Murphy has been targeted by national Republicans since the start of the year, as he got support from Democratic leaders and the White House in his primary victory over U.S. Rep. Alan Grayson. But Murphy has been hampered during the past few weeks as some outside groups stopped running ads for him, a sign that "their resources are better used on behalf of Democratic candidates in other swing states," Jewett said.
Jewett and Binder said Murphy could be further hurt as turnout among black voters may not be as high as it was four years ago when President Barack Obama was re-elected. Binder said Murphy also might not get as big of a boost from Hispanic voters as initially envisioned.
"Two of the Dems' most reliable voting blocs this year aren't as strong as they could be for Murphy here," Binder said. "The African-American vote is down, and the Hispanic vote is much closer to even for Rubio, since he's a Cuban from Miami."
Rubio has sought to distance himself from Trump, but Murphy has repeatedly tried to link the Republican candidates, including over a Newsweek report that a Trump company violated the U.S. embargo of Cuba.
The Clinton campaign has brought Obama into Florida for campaign appearances to help in the presidential and U.S. Senate races. This week, Murphy appeared with civil-rights leader and Congressman John Lewis to promote early voting among African Americans.
But Marian Johnson, senior vice president of political operations for the Florida Chamber of Commerce and a longtime strategist in the state, said Rubio "pulled away from Murphy about 10 days ago and has continued to lead."
"Now, as for what wouldn't surprise me Tuesday? Actually, nothing," Johnson said. "Seriously, given the fact that we are less than a week away and the numbers for third party candidates like (Libertarian presidential candidate Gary) Johnson are not rising as many anticipated, it could lend credit to the argument that Trump is possibly receiving more votes than people are publicly declaring."
After Marco Rubio's presidential bid crashed and as they saw his seat slipping into Democratic hands, Republican leaders in Washington talked Rubio into going back on a repeated pledge not to seek re-election to the U.S. Senate.