In an interview, Stewart, 50, said he will not seek a fourth term as board chair this year and is leaving politics "for the foreseeable future" to focus on his international trade law practice and the business ambitions of his wife, Maria's.
Citing his 16-point loss to Democratic Sen. Tim Kaine in a November election where Virginia Republicans also lost three U.S. House seats, Stewart said his departure from state politics will last "until and unless the Commonwealth is ready for my views on things, and that's not right now, clearly."
As far as the Prince William County board job goes, he said, dealing with land-use cases and the county budget "just isn't exciting for me anymore."
Stewart said he will formally announce his plans Tuesday afternoon in his annual state-of-the-county speech. His decision not to seek reelection sets up a battle for the chairman's seat in increasingly Democratic Prince William that so far includes three candidates: Republican Supervisor Martin Nohe (Coles); Democrat Ann Wheeler; and Donald Scoggins, a moderate Republican who is running as an independent.
An acolyte of President Donald Trump, Stewart embraced a bombastic, often caustic, populist style that attracted right-wing extremists while driving away moderate members of the GOP, whom he once likened to toilet paper.
John Findlay, the state party's executive director, said Republicans are working to repair the intraparty split after a decade of disappointing election losses, which in the past two years were fueled by Trump's deep unpopularity in the Virginia suburbs. That goal took center stage at a party gathering last month where, to the delight of several audience members, Stewart acknowledged that he was retreating from statewide campaigns.
Any political infighting among Virginia Democrats "has just been totally tame, compared to our recent rigmaroles," Findlay said. "Unity and division within our party is definitely a big issue in Virginia."
Stewart's rise to prominence fed off such feuds. He is a political showman who exhibited a zeal for controversy, including raffling off an AR-15 semiautomatic rifle while campaigning for the Senate. From the start, he showed a knack for mining conservative voter frustrations over Virginia's changing landscape.
In 2003, when he successfully ran to become the supervisor in the county's Occoquan District, that meant railing against residential development sweeping through Prince William, leading to clogged roads and crowded schools.
His position on growth in what is now Virginia's second-most-populous jurisdiction eventually changed.
By then, Stewart had latched on to a more volatile issue: illegal immigration.
In 2006, Prince William was passionately divided over a resolution that, initially, directed police to check the immigration status of anyone suspected of being in the country illegally. Stewart championed the measure on his way to winning that year's special election to replace outgoing board chair Sean Connaughton, a Republican.
A decade before Trump would do the same in the presidential race, Stewart characterized the issue as a battle over allowing hardened criminals who were undocumented immigrants into Prince William, a county of suburbs dominated by Washington commuters.
The county's policy, which initially drove away Latino residents, was later amended to apply only to individuals who were taken into police custody. But its more draconian initial version vaulted Stewart onto the national stage, a villain to immigration advocates and a hero to conservatives.
The policy preceded other enforcement measures across the country, including a 2010 Arizona law that requires state police to check immigration status during traffic stops and Trump's own efforts to secure funding for a wall on the U.S.-Mexico border.
"I was kind of a pioneer on that topic," Stewart said, noting that Prince William County has never been successfully sued for racial profiling under its policy.
What kept Stewart in his chairman's seat, however, were bread-and-butter issues affecting county residents.
He championed a $300 million transportation bond in 2006 that has led to road improvements along Route 1 and elsewhere. He also persuaded developers to help pay for dozens of new baseball fields and soccer pitches in Prince William.
But he aimed higher. In 2013, he unsuccessfully sought the Republican nomination for lieutenant governor. In 2016, he briefly chaired Trump's presidential campaign in Virginia. The following year, Stewart capitalized on the racially charged fight over Confederate monuments in Virginia to nearly win his party's nomination for governor.
That battle, which included the Unite the Right rally in Charlotesville that led to the death of Heather Heyer, 32, set the stage for Stewart's victory in the 2018 GOP Senate primary and his decisive defeat by Kaine in November.
In their bitter Senate race, Stewart was saddled by controversies over having associated with right-wing extremists, such as Paul Nehlen and Jason Kessler, who supported his calls to preserve Confederate monuments. Stewart said he cut those ties after learning about the racist beliefs each man harbored.
But their interactions, plus racist social media posts from Stewart advisers during the Senate campaign, led to charges that Stewart himself harbors white supremacists views, which he emphatically denies.
"If you look at my record, find something that I said that was racist, or bigoted or anti-Semitic; you're not going to find it," Stewart said.
His law practice suffered as a result of the controversies, which factored into his decision to leave politics. Last year, Stewart said, the practice lost half of its revenue after a major automobile client severed ties.
"I need to make some money," he said.
But he cited other reasons, as well, familiar to any career politician: lack of sleep, unwanted weight from unhealthful roadside meals, too much time away from family.
"Politics sucks," Stewart said. "On a personal level, it's been a disaster."
In his remaining time as the county board chair, Stewart said, he wants to push for another "really big" transportation bond referendum to fix more roads and a referendum geared toward improving county parks.
He said also has held preliminary talks with the Trump administration about a job in an area related to international trade, although "the problem with these jobs is they don't pay very much."
Otherwise, Stewart said, he wants to help his wife with her plans to build a wedding reception venue on land they own near their Colonial-era mansion, the site of the historic Bel Air plantation.
After that, who knows? He could have a change of heart.
"I watch the news, I get concerned about things, the direction of the country and stuff," Stewart said. "So, I don't want to pull out of it altogether, forever."