Mark Sanford and Corey Stewart make it official: The Republican Party is the Trump Party Donald Trump has moved from outsider to fringe player to leading a movement within the Republican Party. Now he is the GOP. Sanford's loss and Stewart's win prove it.

Jeremy D. Mayer | Opinion contributor

One thing is clear after this week’s primaries: The Republican Party is now officially the Trump Party.

President Trump has moved from being an outsider, to the fringe, to leading a movement within the party, and now it’s over. Republicans will succeed if he does, and they will sink if he fails.

Two key data points prove it: the defeat of Rep. Mark Sanford in a South Carolina House primary and the victory of Corey Stewart in a Virginia Senate primary.

Sanford has always been an unusually principled conservative, and he was at one time so popular in South Carolina that he survived a sex scandal with an Argentinian woman that would have destroyed most politicians. He has also been unusual for not making his peace with Trump after he became the GOP presidential nominee, as so many other Republicans did.

Even after Trump won and began governing, Sanford would occasionally take potshots at POTUS. Most bizarrely, he linked Trump’s rhetoric to the shooting of House Majority Whip Steve Scalise by a mentally disturbed liberal.

Sanford usually supported the president, but he did vote against Trump’s border wall and criticized his aluminum and steel tariffs.

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Sitting presidents typically stay out of congressional primaries, and when they do get involved, they almost always support the incumbent. But a few hours before the polls closed, Trump attacked Sanford in a tweet heard throughout the GOP.

Mark Sanford has been very unhelpful to me in my campaign to MAGA. He is MIA and nothing but trouble. He is better off in Argentina. I fully endorse Katie Arrington for Congress in SC, a state I love. She is tough on crime and will continue our fight to lower taxes. VOTE Katie! — Donald J. Trump (@realDonaldTrump) June 12, 2018

If Sanford had held on for a victory, perhaps a few more "Never Trumpers" would have emerged. Instead, the GOP will move in almost lockstep with Trump now. Some in Congress care about policy, but they all care most about re-election, and Sanford’s fall shows that being on the wrong side of Trump can mean the end of a political career.

In Virginia, Trump’s triumph came differently. In a three-way race for the chance to take on Democratic Sen. Tim Kaine, Republican primary voters chose Stewart, a firebrand who was Trumpy before Trump was.

Stewart first rose to prominence in Virginia politics by attacking immigrants at the local level. He nearly knocked off the establishment Republican candidate for governor a year ago, in part by highlighting his support for Confederate memorials and his endorsement by a white neo-Confederate.

During the presidential campaign, Stewart was so pro-Trump and so against the GOP establishment that he staged an unauthorized pro-Trump demonstration outside the Republican Party’s national headquarters. Even for Trump’s campaign, that was too radical, and Stewart was fired. But his emotional and political connection to Trump persisted.

Trump and Stewart were among the rare prominent Republicans who did not clearly and unequivocally attack the Nazis who marched in Charlottesville, Va., last year. But Stewart went much further than the president, appearing with one of the march organizers before the violence and refusing to condemn the Nazis who marched afterwards.Those Republicans who did, Stewart labeled “weak.”

Who does that sound like?

Exactly.

Virginia’s GOP used to be divided between moderates and conservatives, but with the nomination of Stewart, the white nationalist Trump wing is ascendant.

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Trump’s control over the national GOP has been building for months. At first, it wasn’t clear that he could transfer his popularity with the base into election results.

In Alabama's GOP Senate primary last year, he endorsed Luther Strange, but that didn't help Strange enough to beat the deeply flawed Roy Moore.

And in North Carolina, the first 2018 incumbent Republican to lose a congressional nomination — Rep. Robert Pittenger — was taken out in a race in which both candidates were strong for Trump.

But in the GOP's West Virginia Senate primary last month, Trump successfully blocked the nomination of coal baron Don Blankenship, who had just completed a year in prison. That’s even though Blankenship, with his anti-China rhetoric and conspiracy theories about the GOP establishment, bragged that he was “Trumpier than Trump.” Without Trump’s backing, the Trumpy candidate lost.

How did Trump take over the GOP? Not by careful strategic maneuvering behind the scenes, such as fundraising or palace intrigues. Nor by extraordinary foreign and domestic successes that boosted his popularity with the general public.

Nor did he do it by slavish devotion to Republican ideology. He’s violating 70 years of Republican free trade policy and splitting America from its historic NATO allies such as Germany, France and even Canada.

No, Trump has taken over the GOP by winning the hearts of the primary electorate of the party, the GOP base.

The level of support for Trump from members of his own party at day 500 of his presidency was higher than that for almost any postwar president.

If John Kasich or Jeff Flake or other anti-Trump Republicans think they can knock Trump off in the 2020 primaries, Tuesday’s results show that’s as likely as Hillary Clinton agreeing to serve as Trump’s running mate. So long as the economy remains strong and Trump avoids a foreign policy catastrophe, the love between him and the GOP base is only likely to grow.

Jeremy D. Mayer is an associate professor in the Schar School of Policy and Government at George Mason University in Arlington, Va. He is the author of Running on Race: Racial Politics in Presidential Campaigns 1960-2000 and American Media Politics in Transition. Follow him on Twitter: @JerryDMayer