Trump can insult Haley's supporters all he wants, but he'll need them in November

• Trump couldn't stop himself from offering one final blow to Nikki Haley.
• His underwhelming appeal to her supporters contrasts with Joe Biden's immediate olive branch.

Former President Donald Trump just couldn't help himself. He again chose his MAGA roots in a moment where it would have paid to be more magnanimous to a vanquished foe.

"Nikki Haley got TROUNCED last night, in record setting fashion, despite the fact that Democrats, for reasons unknown, are allowed to vote in Vermont, and various other Republican Primaries," Trump wrote on Truth, his social media platform.

He did include a brief plea for Haley voters to back him, but he also insulted some of them. Trump's decision to offer a parting blow to former UN ambassador Nikki Haley might satisfy his current appetite. But the reality is simple: The former president will need Haley's voters come November.

According to ABC News, 79% of Haley voters have said they would be dissatisfied with Trump as the GOP nominee, per a combination of all the available entrance and exit polling data. The Washington Post cited Quinnipiac University, which found that while a large portion of Republican and Republican-leaning Haley voters would back Trump, 37% would vote for Biden.

To be clear, the former president can take solace in knowing that many more Republicans were disgusted over his 2016 nomination. According to exit polling, nine out of 10 Republicans later backed him that year, as CBS News pointed out. The truth is presidential primaries often end with bitter feelings, but come November most voters return home. Negative partisanship really can do wonders.

Unlike Trump, Biden quickly offered an appeal to Haley's voters.

"Donald Trump made it clear he doesn't want Nikki Haley's supporters. I want to be clear: There is a place for them in my campaign," Biden said in a statement released by his campaign.

Based on how some GOP primary elections worked, some of those voters consider themselves to be Democrats — something Trump never stopped pointing out. Regardless, the GOP primary showed how Trump continues to struggle in suburban areas that often have more educated voters. The overall pools of voters will be different come November, but these struggles highlight one of Trump's weaknesses even as polling shows he's slightly favored at the moment.

This is why Trump's current approach is still a gamble. In many ways, Americans have never seen an election like the one that will now unfold in earnest. A former president has never been criminally charged. Trump faces 91 criminal counts. Only a handful of former presidents have even flirted with trying to retake the White House. Only Grover Cleveland has succeeded.

Haley might have had key policy differences with Trump on foreign policy, such as supporting Ukraine and reassuring North Atlantic Treaty Organization allies. But her challenge was never really about contrasting views. She simply saw what has been transparent from almost every moment after November 2016: Trump can be a major liability to the party he forcibly bent to his will.

It's also hard to see Haley becoming Trump's running mate, a job she's repeatedly said she does not want, or returning to a potential future Trump Cabinet. Presidents and major party nominees have previously used such posts to help soothe tensions.

Haley's decision to not immediately endorse Trump underlines this tension. It could be just a ploy to flex her leverage. It could also be a sign that Trump's past barbs insulting her husband while he was deployed overseas, mocking her name, and questioning her citizenship may never fully heal.

As Haley said, it's now up to Trump, stressing that the GOP needs to be more welcoming.

"I have always been a conservative Republican and always supported the Republican nominee," she said in a speech announcing her withdrawal. "But on this question, as she did on so many others, Margaret Thatcher provided some good advice when she said, 'Never just follow the crowd. Always make up your mind.' It is now up to Donald Trump to earn the votes of those in our party and beyond it who did not support him, and I hope he does that."