U.S. Sen. Bill Nelson has been on the political stage longer than anyone in Florida, since 1972 — the year of Watergate and President Richard Nixon's re-election.That's staying power. It's no wonder that at 74, he's not ready to retire.Nelson, the only Democrat holding statewide office, has led a charmed political life, winning three Senate races against weak Republicans. But that may be coming to an end. He wants a fourth term, and his likely opponent is Republican Gov. Rick Scott."The way I approach an election, I assume nothing," Nelson says. "I run scared as a jackrabbit."He should.Scott, who has won two close races for governor, looks more battle-tested than Nelson, has more money in the bank and is a perpetual campaigner.On the road constantly, the governor held several roundtables in recent weeks and urged local leaders to save Enterprise Florida from that "job-killing" House speaker, Richard Corcoran.So it surely was coincidental that, with no notice, Corcoran invited Nelson to address the House last Thursday while the senator was in Tallahassee."A great privilege and honor," Corcoran called it, as Nelson hailed Corcoran's "courageous stand" for advocating a memorial to the victims of abuse at the Arthur Dozier School for Boys in Marianna.As Nelson left, he and Corcoran warmly shook hands. The message to Scott wasn't very subtle.If Scott and Nelson face each other in 2018, they will be at the top of their parties' tickets.It will fall to both of them to generate enthusiasm to drive up turnout and help candidates for governor, all three open Cabinet seats and the Legislature.Voters appear lukewarm about both of them, but a recent survey by Morning Consult suggests a highly competitive race.Scott also isn't shy about putting his money on the line: about $75 million in 2010 and another $13 million in 2014.His political committee, Let's Get to Work, shows about $2.5 million on hand. Nelson had $1.7 million at the start of this year, according to the Center for Responsive Politics.Nelson was in the Capitol to bolster the spirits of Democratic legislators by telling them that better days are ahead in 2018.That brings us to the heart of the matter: President Donald J. Trump.A race between Scott and Nelson is sure to be a referendum on Trump's first two years in office, in a state he wasn't supposed to win but did by 113,000 votes out of 9.6 million cast.History shows that the president's party often suffers losses in the first midterm election, a trend that should worry Scott, who ran a pro-Trump "Super PAC" and is an enthusiastic Trump supporter.Scott praised Trump last week for promising Florida $1.5 billion a year, about $1 billion more than what the last administration offered, to help hospitals cover unpaid care, a program known as LIP, or Low Income Pool. Unlike President Barack Obama, Scott said, Trump "is willing to work with us."Nelson called that "hypocrisy" by Scott, who turned away $25 billion in federal money by refusing, unlike 32 other states, to expand Medicaid through Obamacare.The LIP must be matched by hundreds of millions of local tax dollars, so "taxpayers are getting it twice in the neck," Nelson said.Scott's office countered that Obama's White House punished Florida by shrinking its LIP money for refusing to expand Medicaid. With Trump, Scott's office says, "Florida was treated fairly."Scott's political fate appears closely tied to Trump. If Trump's popularity improves, it's good for Scott and probably bad for Nelson."We got our hands full," Nelson told Democratic state senators as they wolfed down lunch. "But I'm very optimistic."Nelson said Trump's margin of victory in Florida was in counties where the senator has done well, such as Pinellas, Polk and Volusia, where he'll need to do well against Scott -— who knows how to win in nonpresidential election years.Of Trump voters, Nelson predicted: "There's going to be some buyer's remorse."Contact Steve Bousquet at [email protected] Follow @stevebousquet.