Corey Stewart, who narrowly lost the GOP nomination for governor to Ed Gillespie last month, plans to challenge Sen. Tim Kaine (D) in 2018. (Linda Davidson/AP)

Corey Stewart declared the “kinder, gentler Republican” extinct Thursday as he announced his plan to launch a “vicious” campaign to unseat Sen. Tim Kaine (D-Va.) in 2018, with all the bombast that brought the Prince William supervisor within a hair of winning his party’s nomination for governor last month.

“I’m going to run the most vicious, ruthless campaign to dethrone Tim Kaine from the United States Senate,” said Stewart, not quite a month after losing the gubernatorial nomination to Ed Gillespie by 1.2 percentage points. “It’s time that Republicans take back that seat; it’s time that we have a senator who supports the president. Not trying to obstruct his way.”

The move pits Stewart, a President Trump supporter who celebrates the Confederacy and slams illegal immigrants, against Hillary Clinton’s former running mate in a state that often embodies the nation’s political crosscurrents.

Stewart, who has boasted that he was “Trump before Trump was Trump,” said Democrats partly blame Kaine for losing the presidential race and called him a “nervous Nellie.”

Kaine dismissed the criticism, but in a subtle barb announced just ahead of Stewart’s news conference that he and Sen. Mark R. Warner (D-Va.) had secured $4.2 million in federal funding to preserve Civil War-era battlefields.

“Right out of the gate, Corey Stewart is more focused on name-calling than improving Virginians’ lives,” Kaine campaign adviser Jenny Nadicksbernd said in a statement. “Senator Kaine will continue working with both Democrats and Republicans to build economic opportunity through better skills, jobs, and wages and protect health care for all Virginians.”

Stewart’s announcement was met with silence from state GOP leaders and elected officials, who said they are focused on making sure Gillespie is the first Republican elected in November to statewide office since 2009.

But some Republicans said a Stewart candidacy threatens to damage the GOP brand and derail Gillespie’s efforts to appeal to moderate Republicans and independents, especially those in vote-rich northern Virginia.

“Corey Stewart will be out there saying and doing ridiculous things that make the party look bad and put Republican candidates in a terrible position,” said Bill Bolling, a former two-term Republican lieutenant governor. “This is really a nightmare for the Republican Party.”

From the front yard of his Woodbridge home, Stewart announced his campaign with his smiling wife by his side, but without any other elected officials.

He said he was launching his campaign a year in advance to start raising money for what could be an expensive race. Stewart, who struggled for funds in his gubernatorial bid and was outspent 3-to-1 by Gillespie, embraced controversial stances as part of a deliberate strategy to garner media attention and inflame voter passion. He gave away an assault rifle at a shooting range, unfurled Confederate flags at rallies and got into a Twitter war with musician John Legend, among other things.

Asked whether he would need support and resources from state and national party officials, Stewart was defiant. He said he had not consulted with anyone before deciding to run on the heels of his strong showing in the Republican gubernatorial primary election.

“They’re less important than they used to be; that’s for darn sure,” he said. “The party is going to have start waking up and realizing that constituents, conservative Republicans, are looking for a more aggressive populist candidate. I’m talking about someone who can actually appeal to people, to average working-class people and bring them in.”

Stewart acknowledged that Kaine helped Clinton win Virginia — the only Southern state she carried. But he later said that Democrats “aren’t that enthralled” with the senator.

Republicans have said running nationwide with Clinton forced Kaine to take positions — opposition to the Trans-Pacific Partnership as well as offshore drilling — that are out of step with Virginia voters.

Yet polls show Kaine — a former governor and lieutenant governor — is popular in the state with a 58 percent job approval rating, while Trump’s approval ratings were at 36 percent in a Washington Post-Schar School poll in May.

Geoffrey Skelley, a political analyst at the University of Virginia Center for Politics, said the statewide landscape favors Kaine.

“In an alternate universe where Clinton won, people like Barbara Comstock or Dave Brat would probably be looking much harder at running for Senate in 2018,” he said, referring to Republican members of Congress from Virginia. “But given that Trump won and is very unpopular in the state of Virginia, my guess is Tim Kaine is very happy to face Corey Stewart.”

“Stewart nearly won a primary despite a serious resource shortage, so that might suggest that a primary is better for him,” Skelley said. “But the dynamics of the 2018 GOP candidate field will matter a great deal.”

John Whitbeck, chairman of the Virginia GOP, said he anticipates a crowded field.

“He’s not going to be the only candidate, so we’re not even worried about that right now because we have a tremendous challenge ahead of us to win three statewide races,” Whitbeck said, referring to the November election when Virginia voters will choose a governor, lieutenant governor and attorney general.

Stewart is the first Republican to announce his intention to challenge to Kaine. Carly Fiorina, the former GOP presidential candidate, conservative radio host Laura Ingraham and retiring state Del. Jimmie Massie III (Henrico) have said they are considering joining the race. The party will decide its nominee in a primary election next year.

In hypothetical matchups, Kaine would defeat Fiorina by 24 points and Ingraham by 21 points, according to an April Quinnipiac University poll.

In an interview with The Washington Post last month, Stewart offered a glimpse of how he might conduct himself with Kaine through some blunt advice for Gillespie in his contest against Democratic Lt. Gov. Ralph Northam.

“Ed, if you’re listening to this: Nobody cares that your dad owned a grocery store,” Stewart said, mocking Gillespie for a “boring” stump speech line geared toward blue-collar voters and a “Mr. Rogers sweater” Gillespie wore in a campaign ad. “Sometimes, you just gotta be yourself. Just do it.”

Stewart’s strong showing in last month’s gubernatorial primary shocked state party leaders and political observers who had dismissed him as a fringe candidate.

The native Minnesotan’s embrace of “Southern heritage” issues and disdain for the Republican establishment drew support from white nationalists and many Trump voters in the western part of the state as well as southwest and Southside Virginia, and his own Prince William County.

Stewart served as Trump’s Virginia campaign chairman for much of last year, until he became too divisive even for the Trump campaign and was fired.

Despite some of his inflammatory rhetoric about immigrants, Stewart has navigated the changing demographics of his county with some success.

He recently regained favor with local Muslims upset about his support for Trump when he championed the building of a new mosque in Gainesville — a project that tapped into anti-Muslim sentiments before it was approved after an all-night meeting last month in a 5-4 vote.

But Stewart’s insurgent gubernatorial campaign did cost him some support — four of the five Republican supervisors who serve with Stewart came out for Gillespie, abandoning plans to stay neutral.