Wisconsin Republican Sen. Ron Johnson officially announced Sunday that he is running for reelection, parting ways with a 2016 promise to only serve two terms because he believes the Democrats’ "complete takeover of government" has put America in "peril."

Johnson announced in The Wall Street Journal that he will run for a third term in Wisconsin – a key battleground state that President Biden narrowly carried in the 2020 election.

WISCONSIN GOP SEN. RON JOHNSON TO RUN FOR REELECTION, DEFYING TWO-TERM PLEDGE: REPORTS

Senator Ron Johnson

Sen. Ron Johnson speaks during a hearing of the Senate Foreign Relations Committee on U.S.-Russia policy at the Capitol on Dec. 7, 2021. (Alex Brandon/Pool/AFP via Getty Images)

"During the 2016 campaign, I said it would be my last campaign and final term," Johnson wrote. "That was my strong preference, and my wife’s – we both looked forward to a normal private life. Neither of us anticipated the Democrats’ complete takeover of government and the disastrous policies they have already inflicted on America and the world, to say nothing of those they threaten to enact in the future.

"Nor did we anticipate the pandemic, the government’s failed response to it, the loss of freedom that has resulted, and the tyrannical approach taken by the elites who have created and maintained a state of fear that allows them to exercise control over Americans’ lives," he continued. "Instead of everyone working to achieve the goal President Biden stated during his inaugural address – unifying and healing America – it feels as if our nation is being torn apart."

"I believe America is in peril. Much as I’d like to ease into a quiet retirement, I don’t feel I should," he added. "Today, I am announcing I will continue to fight for freedom in the public realm by running for reelection. It is a decision I haven’t made lightly."

Sen. Ron Johnson, R-Wis.

Sen. Ron Johnson talks to reporters on Capitol Hill in Washington, Feb. 12, 2021. (AP Photo/Susan Walsh, file)

Johnson warned that millions of dollars will be spent trying to "destroy" his campaign, and that the mainstream media and Big Tech will collude with Democrats in an effort to defeat him.

"Their path, paved with false hope and greater dependency, always leads to tyranny. We cannot let them win," he concluded.

Sen. Ron Johnson (R-WI)

Sen. Ron Johnson speaks with reporters after attending a luncheon with Senate Republicans at the U.S. Capitol on Oct. 7, 2021. (Anna Moneymaker/Getty Images)

Wisconsin is one of a handful of contests that could ultimately decide which party controls the currently evenly divided 50-50 Senate.

Johnson – an ardent supporter of former President Trump – would have a good chance of winning reelection in Wisconsin, a state Biden won by less than a percentage point in 2020. Trump narrowly won Wisconsin in 2016.

The National Republican Senate Committee issued a statement Sunday endorsing Johnson’s campaign.

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"Sen. Ron Johnson is a good friend and a fierce colleague who’s not afraid to stand up for what’s right," said NRSC Chairman Sen. Rick Scott, R-Fla. "He is a tireless advocate for small businesses and the hardworking people of Wisconsin. He brings commonsense solutions to the Senate and always fights to protect and defend the security of our homeland and our priorities abroad, and deeply cares about the betterment of his state. 

"While Wisconsin Democrats trip over themselves to prove who’s more liberal, Sen. Johnson continues to demand accountability in Washington and deliver results for Wisconsinites," Scott said. "The NRSC is proud to endorse Sen. Johnson’s reelection campaign. He has won this battle twice before, and he will win it again."

Fox News' Kyle Morris contributed to this article.