Talk about raising the stakes: Hillary Clinton says the “whole world” is pulling for her to defeat Donald Trump in November’s election.

In a fundraising email Wednesday morning, after Mr. Trump ousted his final major opponent the night before, Mrs. Clinton’s team said it was “unimaginable” that the maverick businessman would capture the GOP nomination.

“I don’t know how else to say it: The whole world is counting on us to win this thing. And we owe it to them to step up,” wrote Clinton staffer Christine Reynolds.

Mrs. Clinton, who has advocated for cutting the influence of money in politics, is nonetheless hoping her own prolific fundraising can be an advantage as she faces Mr. Trump, who so far has done little to actively solicit others’ money.

But Mr. Trump signaled Wednesday morning that he may be preparing to change tactics, saying he wasn’t sure whether he will keep self-funding his campaign.