By Maegan Vazquez and Eric Bradner, CNN

(CNN) -- Florida Republican Gov. Rick Scott is running for the US Senate, he told Politico in an interview published Monday, setting up a serious challenge to the state's incumbent Democrat, Bill Nelson.

"You're probably surprised, but I'm going to announce I'm running for senator," Scott told Politico, joking that it's one of the worst kept secrets in the state's political scene. "You're shocked, right?"

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.

Scott's campaign is teasing a "big announcement" on social media. A Facebook live video published Sunday says: "TOMORROW 10 AM." Further fueling the speculation: Scott's chief of staff, Jackie Schutz Zeckman, announced her resignation last month, potentially positioning her for a role on a Senate campaign.

Scott is 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.