WASHINGTON — Outspent on the air and out-muscled on the ground, Sen. Bill Nelson takes comfort in the bottom line: Polls show he and Gov. Rick Scott remain effectively tied.

"By the way," Nelson said while riding the Senate subway on a recent afternoon, "my name ID is coming up because he keeps repeating it so much." The 75-year-old, three-term Democrat laughed and said what matters is the long run.

Democrats in Washington and Florida aren't laughing. They are increasingly nervous as Scott and Republican allies have unleashed a flood of money into TV and online ads — roughly $20 million so far, more than Nelson's 2012 opponent spent on the entire campaign — and maintain a superior organization that spares no opportunity.

As the World Cup began Thursday, Scott released his latest ad targeted at Hispanics. "In Florida, we celebrate because we come from different parts," he says in Spanish. "And this great state is now our home. Here we are united in our love for this great sport."

Scott is employing the same scorched earth strategy he used to win office twice before: Blanket TV, define the opponent in starkly negative terms, campaign nonstop and never go off script. If things get tight, spend millions more.

"Charlie Crist was going to win the election with a week to go, and Rick put in $12 million of his own money, and we saw the lead shrink from three points, to two, to dead heat, to loss," Orlando trial lawyer John Morgan recalled of Scott's narrow 2014 victory. "You can never underestimate the power of that money, and Rick Scott has got eight years of doing a job for Florida and that's also going to be tough for Bill Nelson."

Democrats generally have the advantage of running in a midterm election that historically favors the party not controlling the White House — incumbents like Nelson do especially well — and President Donald Trump continues to motivate the Democratic base. But the narrow path for Democrats to reclaim the Senate runs is challenged by states that Trump won, including Florida.

Nelson is suddenly one of the party's five most vulnerable members in the country, and the nation's third-largest state is by far the most expensive state of those five. A victory for Nelson will be extremely costly and could drain resources from Democrats elsewhere.

"Outwardly they project confidence, but they're worried," said Jennifer Duffy, an analyst with the nonpartisan Cook Political Report. "There are days when I think he's the most vulnerable incumbent."

The spotlight on Nelson and Florida has only intensified as Democratic senators in Pennsylvania and Ohio have solidified positions against weaker Republicans. And no one will face the mountains of money that Scott, a millionaire former hospital executive, can marshal.

"He's running probably the best campaign in the country from the nuts and bolts perspective," said Sen. Cory Gardner, the Colorado Republican who heads the GOP's Senate election effort, who took a shot at Nelson's slow start.

The Democrat has stepped up campaign appearances and has seized national issues to draw contrasts with Scott, lately accusing him of hurting Floridians by not expanding Medicaid under Obamacare, which is no longer a campaign liability.

But Nelson can't afford to match Scott on TV and risks being defined on Scott's terms. Scott's ads have called for term limits and attacked Nelson as a career politician, one comparing him to a broken down Ford Pinto, the compact car that became the butt of jokes and a target of lawsuits.

"Rick Scott is spending very real dollars on what are clearly poll-tested messages. Most polls have the race at tied or leaning Rick Scott. Any incumbent in that position should be worried," said Steven Vancore, a Democratic pollster in Florida.

Scott's has already forced national Democratic groups to spend resources on Florida.

"It's uncomfortable for the Nelson people," said Steve Schale, a Democratic strategist who ran Barack Obama's 2008 Florida campaign and was twice opposite Scott in the 2010 and 2014 races for governor. "Scott's ability to get on TV early really makes a difference. When you're on the other side, you have to ask yourself, is it better to define yourself early or not?"

The race, however, will not be decided by TV ads but by Trump, Schale argues. "It's going to come down to what the national mood is in October. If the voters are upset with Donald Trump, they are not going to vote for Rick Scott."

Scott has conspicuously avoided mentioning Trump on the campaign trail but it wasn't long ago they were taking selfies together and visiting at the White House and Mar-a-Lago. "The videotape exists," Schale said.

Democrats also point out that Scott's previous election wins were exceedingly narrow (1.2 percentage points in 2010 and 1 percentage point in 2014) despite vastly outspending rivals Alex Sink and Crist.

"All Gov. Scott has got is a lot of money," said Sen. Chris Van Hollen of Maryland, who oversees Senate elections for Democrats. "You can say, 'Well, a win's a win,' which is true. But very importantly, both of those years were huge Republican years. Now he's up against someone who's been a real leader for Florida."

Nelson hasn't gone up on TV but has gotten help from Senate Majority PAC, an outside group that spent $2.2 million on a biographical ad. The group, which has also reserved TV time for after Labor Day, last week released an online ad that mimicked one of Scott's showing Nelson through the years: highlighting points in Scott's business and political career that have been marked with controversy, including the $1.7 billion fine his former hospital company paid to settle a Medicare fraud investigation.

Democrats have also raised conflict of interest questions based on Scott's personal wealth growing during his time in office (Scott has put his money in a blind trust that remains the subject of a lawsuit). On the campaign trail, Scott has faced negative news coverage over alleged cronyism and coziness with special interests that have fueled his political committees.

Hours after Scott released his World Cup ad, Nelson announced his first Spanish-language spot, though it was intended for social media and came amid criticism that his outreach to a key constituency is lagging.

Nelson hasn't had to work this hard in his past two elections against lightweight opposition. Scott as governor has higher visibility than Nelson, whose Senate career lacks a defining moment. Former Democratic state Sen. Chris Smith of Fort Lauderdale worries about a growing number of younger independent voters who are newly registered and don't know Nelson.

On the other end, older voters appear to be favoring Scott. An AARP/Politico poll released last week showed Scott with a 9 percentage point lead among voters 50 or older — highly reliable voters. It also showed Trump fares better among that group than the voting population at large.

Morgan, Florida's leading advocate for medical marijuana use, said independent voters may be the key to the race. If they vote for divided government — a Republican president and a Democratic Senate — it's a good sign for Nelson.

"As much as Republicans want Trump and Democrats don't want Trump, the independents want a check on each of the branches," Morgan said. "It's going to be a dogfight."

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