Two races – one in SC and one in NY – will put Trump to the test on Tuesday

President Donald Trump is tweeting out endorsements, he’s rallying his supporters — and this week he is again testing his ability to move Republican votes when his name is not on the ballot.

On Tuesday, two very different slices of Trump’s base will head to the polls to decide whether to back the president’s chosen candidates, an early indicator of Trump’s ability to turn his supporters out ahead of the fall midterm campaigns.

In New York, Trump has blessed incumbent Rep. Dan Donovan in his tight Staten Island-area race against former Rep. Michael Grimm. Grimm was briefly jailed for felony tax fraud but retains a base of support in this more blue-collar district, where Trump is also embraced as a native son.

And in deeply conservative, heavily evangelical South Carolina, where voters appreciate Trump’s Supreme Court pick, Trump will rally Monday for Gov. Henry McMaster, who faces a competitive primary runoff against businessman John Warren.

“I can’t think of another person in the party who has more credibility with primary voters than President Trump,” said Scott Jennings, a veteran GOP strategist. “If anybody’s word matters, it will be his.”

But in past elections this cycle, Trump’s word hasn’t always mattered so much, with several of his anointed candidates losing in high-profile races--from Luther Strange in an Alabama Senate primary, to Rick Saccone in a congressional district Trump previously won by around 20 percentage points. The results Tuesday will help political operatives gauge how effectively Trump can transfer the energy of his base to other candidates, now that the midterms are less than five months away.

“If Donald Trump were on the ballot, the McMaster race would probably be over, he’d have won,” said Katon Dawson, a former chair of the South Carolina Republican Party. “He’s not.”

Trump’s ability to bestow his brand on other Republicans has serious implications for this fall’s elections, as GOP contenders confront what many see as a lack of enthusiasm among right-of-center voters fueled by the fact that Trump’s not on the ballot and the GOP-controlled Congress hasn’t achieved many of its priorities. On the other side, Democrats and progressives are providing significant evidence of a motivated activist base mobilized against Trump.

At a minimum, Republican strategists and activists in New York and South Carolina say that when it comes to stoking GOP energy, a Trump endorsement can only help, even if it’s hardly a guarantee of victory.

Earlier this month, a poll from NY1/Siena College — the timing of which didn’t fully capture any Trump endorsement bounce—found Grimm leading Donovan by 10 percentage points, and Grimm has devoted fans who have circled the wagons around him. National Republicans continue to see the race as extremely competitive, with an unpredictable primary electorate.

But pro-Donovan forces say Trump’s tweeted endorsement — and additional support from his presidential campaign, including a supportive video from daughter-in-law Lara Trump, a senior campaign adviser — injected a new sense of energy and confidence into the congressman’s campaign, while also helping to blunt Grimm’s accusations that Donovan is an establishment Republican who doesn’t really stand with Trump.

“Donald Trump is loved on Staten Island, and particularly in a Republican primary, it could make or break the race, and I think it has given Danny the momentum he needs to win,” said Republican Assemblywoman Nicole Malliotakis, whose state assembly district is in the Donovan congressional district. “It has the ability to neutralize Grimm voters and push undecided toward Donovan. In a race where the polls show it being tight, that makes the difference.”

And in a Republican primary in socially conservative South Carolina, there is no greater gift than a Trump endorsement.

Trump endorsed McMaster well before the primary. But last week the president detailed his home-stretch runoff plans for the governor: “I will be going the Columbia, South Carolina, on Monday night to do a campaign speech for one of my very early supporters, a man who truly loves the people of South Carolina, Governor Henry McMaster,” he tweeted. “Henry worked so hard & was so loyal to me that I look forward to reciprocating!”

“Him going into South Carolina is a big deal for Henry, a rally right before the election is definitely going to juice some turnout, being a runoff like this,” said Terry Sullivan, Marco Rubio’s former presidential campaign manager, who has extensive experience in South Carolina politics. “The other candidate, Warren, is trying to portray himself as an outsider, Trump-esque kind of candidate. This steals a lot of oxygen from that in a state where, in a primary, Donald Trump is super popular there.

Trump comes to South Carolina emboldened. Two weeks earlier, he intervened on Katie Arrington's behalf in her quest to beat incumbent Republican Rep. Mark Sanford in the First Congressional District's GOP primary. Arrington prevailed, and Trump is taking credit for helping make it happen.

But despite the narrative that Sanford lost because Trump backed his opponent—hours before polls closed—several Republican political office holders, strategists and observers in the state all told McClatchy that Trump's endorsement was only part of the equation.

They say Sanford, who had never before lost an election, just didn't take Arrington's challenge seriously until it was too late. Sanford also narrowly won his primary two years ago, which should have been a sign that he was weaker among constituents than he appeared. (In an interview with McClatchy, Sanford disputed characterizations that he didn't take Arrington's challenge seriously, and said that Trump was indeed the defining factor in his defeat.)

If Trump didn't single-handedly deliver Arrington the election, it's unclear whether he can significantly tip the scales for McMaster, who always treated his primary race as competitive. Trump's endorsement alone wasn't enough to help McMaster garner more than 50 percent of the vote in his crowded primary field, forcing the governor to compete in a runoff.

"The Donald Trump effect is not transferable," said Matt Moore, a political consultant and former South Carolina Republican Party chairman. "He is a once-in-a-lifetime political phenomenon and we are seeing that in the governor's race in South Carolina. Henry McMaster has done almost everything but literally hugged Donald Trump and he couldn't get over 50 percent in the primary."

Indeed, in other significant races where Trump has actively campaigned — most prominently the special election in Alabama, in both the primary and the general election, and Saccone’s Pennsylvania contest — Trump’s candidates suffered defeats.

“If any sitting president comes in and endorses a candidate of their own party in a primary, that’s usually 100 percent success rate, that’s a huge deal,” Sullivan said. “If Barack Obama had done that in a Democratic race or George Bush did in a Republican race, that’s a slam dunk. It should be 100 percent success rate. Obviously it has not been for them.”

Dawson still thinks McMaster has a “very good chance” and called Trump an “asset” for him. But he drew a different comparison to Obama, who won reelection — though in between, Republicans romped in the midterm campaigns, in large part by campaigning against him.

When Trump and Obama were on the ballot, their bases were motivated, he said. But as Dawson reflected on the last year of special elections, he said, “I haven’t seen the president’s hardcore base mobilize, much like President Obama’s, except when he was on the ballot.”

Katie Glueck: 202-383-6078, @katieglueck
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