A prominent Republican donor who gave nearly $6 million to an anti-Donald Trump super PAC during the primary has reversed course, and is now pledging to help boost the GOP presidential nominee in the last leg of his campaign against Hillary Clinton.

Joe Ricketts, the founder of TD Ameritrade and an early supporter of Wisconsin Gov. Scott Walker's presidential bid, plans to contribute at least $1 million to a super PAC supporting Trump, the Wall Street Journal reported late Monday evening.

Ricketts' stunning reversal comes as Trump has tightened the gap between himself and Clinton in key battleground states and national polls, and made a concerted effort to stay on message during interviews and his rallies.

But even as Trump shows off a refined approach to his campaign, Ricketts' decision to pour money into a pro-Trump outside group is especially noteworthy considering the White House hopeful once threatened the Ricketts' family.

I hear the Rickets family, who own the Chicago Cubs, are secretly spending $'s against me. They better be careful, they have a lot to hide! — Donald J. Trump (@realDonaldTrump) February 22, 2016



"It's a little surreal when Donald Trump threatens your mom," Ricketts' son, Todd, told reporters during a press conference in March.

It is still unclear where the Ricketts plan to lend support to Trump as there are a limited number of super PACs backing the GOP hopeful that are seen as legitimate. The family could instead make contributions to groups that oppose and are running ads against Clinton.