Washington CNN  — 

Florida Republican Gov. Rick Scott launched his long-anticipated challenge to Democratic Sen. Bill Nelson on Monday, officially kicking off one of 2018’s most important – and likely most expensive – races.

Scott announced his entry into the race in interviews and a video posted on his social media accounts reviewing his two terms as governor.

“I never planned to fit in, and I won’t fit in in Washington, either,” Scott says in the video. “It’s time to shake that place up. We don’t need another politician in Washington. It’s full of politicians, and that’s why it’s broken.”

Scott has served in the governor’s mansion since 2011 and has long been courted to join the Senate race.

Asked if he considers himself a “Donald Trump Republican,” Scott told Politico: “I consider myself Rick Scott. I don’t consider myself any type of anything.” The governor would not tell the publication whether the President would campaign for him.

In a statement following Scott’s announcement, Nelson said: “I’ve always run every race like there’s no tomorrow – regardless of my opponent.”

Nelson later told CNN’s Wolf Blitzer Monday afternoon that “there are so many differences” between himself and Scott.

“I think Rick Scott will say and do anything to try to get elected, but I’ve always thought that if you just try to do the right thing, the politics is going to take care of itself,” he said.

Scott was the last major Republican recruiting target on a 2018 Senate landscape that features Democrats defending seats in 10 states that Trump won in 2016. He’s been viewed as the only Republican with a chance of seriously challenging Nelson.

Scott previously won two close races for governor. He’s also shown he is willing to spend tens of millions of dollars of his own money on campaigns – a trait that is especially important in Florida, a large and expensive state for television advertising.

Anticipating Scott’s entry into the race, Democrats have spent months readying their attacks on his two terms in Tallahassee.

The Senate Majority PAC, a Chuck Schumer-aligned super PAC, released a digital ad over the weekend as part of a six-figure campaign this week blasting Scott for cutting businesses’ taxes while raising property taxes and slashing education funding.

“History has proven that if you want to predict how Rick Scott will act, figure out what will benefit his political career and his bank account,” said J.B. Poersch, the super PAC’s president.

In a memo sent to reporters Monday morning, Democratic Senatorial Campaign Committee executive director Mindy Myers previewed the party’s line of attack against Scott by calling him “self-serving and dishonest” and saying he is “looking out for himself at Floridians’ expense.”

Myers said Scott’s actions as governor have made him $46 million richer. She also highlighted the deaths of 14 seniors in a nursing home during Hurricane Irma and accused Scott of deflecting blame for the Parkland shooting and the Florida International University bridge collapse that killed six people.

Myers pointed out that Scott’s gubernatorial wins in 2010 and 2014 came in tight races, and that Florida has seen a shift in Democrats’ favor since Trump took office – including wins in the St. Petersburg mayoral race and two hotly contested state legislative special elections.

“Scott’s self-serving political brand, his administration’s failures and a hostile political environment will all cripple his campaign,” Myers said.

South Dakota Republican Sen. Mike Rounds signaled support for Scott on CNN’s “New Day” Monday morning, though stopped short of a full endorsement.

“Senator Nelson is a friend of mine. He is a hard worker. At the same time we need votes,” he said. “I would welcome (Scott’s) inclusion in the race.”

This story has been updated with additional information.

CNN’s Eli Watkins contributed to this report.