“For a variety of reasons, Rubio will be tough to beat — whether because it is an off-year election, his Miami roots or his profile — that’s hardly a surprise to anyone and I believe that is why there is an absence of big names lining up early,” said Steve Vancore, a veteran Democratic pollster and strategist…

The reasons for the hesitance to take on Rubio are myriad. Among the biggest issues are the astronomical cost of running a statewide Senate race in Florida to the sorry state of the state Democratic Party, which typically fares poorly in midterm elections. But none worry Democrats as much as the bilingual Cuban-American’s ethnicity and his home base in Miami-Dade.

The state’s most populous county, Miami-Dade is where Democratic candidates need to run up the score to offset losses elsewhere in the state. And as Florida’s top Hispanic politician, Rubio begins there with a critical advantage.

“Any Hispanic Republican statewide messes the math up terribly for Democrats,” said Eric Johnson, who advised Rubio’s 2016 Democratic opponent, former Rep. Patrick Murphy. “Once a Republican starts taking a chunk of the Hispanic vote, they’re almost unbeatable. And with Marco being from Miami-Dade County, it’s just really difficult to get there.”