Once former President Donald Trump racked up enough primary wins and delegates to secure his position as the GOP's presumptive presidential nominee, nearly all high-profile Republicans, including his rivals in the bitter primary contest, issued endorsements of his candidacy for a second term in the White House.

There is one notable exception, however, in that former U.N. Ambassador Nikki Haley, the last of his rivals to drop out of the primary, has not yet endorsed her former boss' re-election bid, and speculation is growing that she will soon be forced to decide one way or another, the Associated Press reported.

The reason for that lack of endorsement remains unclear, though there are rumors that it has to do with her apparent exclusion from consideration as a possible vice-presidential candidate and running mate for Trump.

Trump says Haley "not under consideration" to be his VP pick

Axios reported earlier this month that despite the public insistence to the contrary by many of former President Trump's top aides and surrogates, unnamed sources allegedly close to or within the campaign claimed that Haley was under active consideration to be his VP pick, even though the pair had a "chilly" relationship following the brutal primary fight.

Those sources said Trump would pick Haley if he believed that doing so would help him win the presidency, avoid a possible conviction and prison sentence, and cover his campaign costs and legal bills via her substantial network of deep-pocketed donors.

Yet, just one day after that report was published, Trump posted on his Truth Social account, "Nikki Haley is not under consideration for the V.P. slot, but I wish her well!"

Will she or won't she endorse Trump?

The AP report on Haley's lack of an endorsement of Trump could soon reach a point where she would feel compelled to make a move one way or the other, each with its own benefits and disadvantages.

On the one hand, a Haley endorsement of Trump would likely serve to keep her in the good graces of the GOP electorate and protect her status as a top Republican for future election cycles, if not even win her a key position in a second Trump administration.

On the other hand, though, not endorsing Trump might help maintain the not-insubstantial coalition of support she has built among independent, moderate, and "NeverTrump" Republican voters. That support, and the donor dollars that come with it, could be diminished or vanish completely if she is viewed as having given in to her bitter rival.

The AP observed that even though Haley dropped out of the race and ended her candidacy in March, she has continued to make a strong showing in the largely meaningless primary elections that have been quietly held since then, earning around 20% support in states like Arizona, Indiana, and Maryland, and is expected to do the same in Kentucky's upcoming contest.

Biden trying to win over Haley's anti-Trump supporters

None of this is playing out in a vacuum, either, as the AP reported that President Joe Biden's campaign has attempted to further drive a wedge between Haley and Trump as a means to draw over at least some of Haley's anti-Trump support.

The National Desk reported in late March that the Biden campaign released an ad that featured clips of Trump insulting Haley and included an overture from the incumbent president himself, who said, "Nikki Haley voters, Donald Trump doesn’t want your vote. I want to be clear: There is a place for you in my campaign."

In her speech to announce the end of her campaign, Haley herself declined to encourage her supporters to shift over to the presumptive GOP nominee and instead placed the onus on the former president, as she said at that time, "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."

How Haley ultimately decides to handle the Trump endorsement question -- to say nothing of the rumored possibility of a Biden endorsement -- will likely prove consequential for her future political career regardless of whichever direction she decides to go.