On Wednesday, U.S. Senator Marco Rubio, in breaking an earlier pledge to not run for two offices in the same year, announced he was running for re-election after all. The likelihood of the Republican senator retaining his seat seems high. However, numerous hurdles, including immigration and his reliability to show up for work, could complicate Rubio's quest for the nomination and election in November.

On paper, Rubio appeared to be the future of the GOP and was touted by some as a "stealth" front-runner in the presidential contest. However, his youth and Cuban heritage did not translate to much electoral success, with much of his support coming from the party establishment and the conservative media class. Facing several obstacles, Rubio won only the Minnesota and Washington, D.C. caucuses and the Puerto Rico primary and suspended his presidential campaign in mid-March.

His national career seemingly over, Rubio then reneged on a promise to leave the U.S. Senate in favor of his presidential run. Any political damage Rubio incurred on the presidential trail will be first decided at the August 30 primary.

With his announcement, the only remaining serious challenger to Rubio on the Republican side of the Senate race is businessman Carlos Beruff, who is described in The Hill as a "Trump-like" candidate. Calling for a temporary ban on Muslim immigration, Beruff has also used the expression "America First" in a campaign ad, and recently told National Review that even with Rubio in the race, he is "all in."

If Trump becomes a factor in the Florida Senate race, Rubio could be challenged on his conflicting statements about Trump, ranging from calling him a "con man" to approvingly saying the presumptive nominee should not change his approach for the general election. Trump won the Florida presidential primary with 46%, far ahead of Rubio's 27% second-place finish, thus making the New York businessman a formidable figure in the state.

Perhaps the most daunting challenge will be the question of why Rubio should be returned to a legislative body when he had the most absences and missed votes of any member of the Senate. Anonymous reports have said Rubio "hated" the Senate, though the senator himself has only used the word "frustrated" to describe life in the upper chamber.

Rubio defended his spotty attendance by noting that other legislators running for president faced the same predicament of voting or campaigning. However, Rubio ranked in the 90th percentile and higher numerous times prior to running for president, including his first year in office. The Tampa Bay Tribune reported about Rubio's absenteeism:

"He has missed 60 percent of Foreign Relations hearings since joining the Senate despite making his committee experience a centerpiece of his qualifications for president."

Immigration, one of the factors credited for Rubio's demise as a national Republican figure, could also surface in a heated primary with Beroff. Months before the Orlando nightclub shooting, two-thirds of Florida Republicans already favored a temporary ban on Muslim immigration, such as the one proposed by Trump and Beroff.

The topic of immigration restriction also is not unprecedented in toppling an incumbent. In 2014, Dave Brat upset then-House Majority Leader Eric Cantor in part over the latter's immigration policies.

Disappointing presidential campaigns have occasionally hurt politicians in their subsequent re-elections. After winning the Iowa Straw Poll in 2011, Michele Bachmann's presidential campaign declined precipitously. She barely won re-election to the House and retired instead of running for additional terms.

The winner of the Republican primary is likely to face either Alan Grayson or Patrick Murphy, two Democratic congressmen facing off in their party's primary. Most polling at this point shows Rubio ahead of either Grayson or Murphy, but no prospective candidate in the Senate race reaches 50% in most surveys.

Florida operates a closed primary, so partisanship may dominate the primaries. However, with 10-30% undecided for the general election, independents and moderates may get a voice in deciding whether Sen. Rubio's path will be rewarded with another term.