Donald Trump assumed control of the Republican Party on Wednesday as its presumptive presidential nominee after Ohio Gov. John Kasich exited the race, moving swiftly to consider vice-presidential prospects and plan for what is expected to be a costly and vicious six-month battle for the White House against Democrat Hillary Clinton.

Trump, who has proudly touted how he has self-funded his campaign, said he would begin actively seeking donations for his campaign and raise money for the national party, part of the arduous task of coalescing a party deeply divided.

Party leaders are scrambling to stave off a parade of prominent Republicans endorsing Clinton, but already there were notable defections. The two living former GOP presidents, George H.W. Bush and George W. Bush, have no plans to endorse Trump, their spokesmen said.

In the swing state of Nevada, Gov. Brian Sandoval, a moderate Republican and rising Latino star, said he plans to vote for Trump despite their disagreements on some issues. But Sen. Dean Heller (R-Nev.), who is up for re-election in November, said that “I vehemently oppose our nominee” because he disparaged women, Hispanics and veterans — although Heller insisted he would not vote for Clinton.

Meanwhile, Clinton called Trump “a loose cannon” and invited Republicans and independents seeking an alternative to join her. “Let’s get off the red or the blue team. Let’s get on the American team,” she told CNN.

Some Republicans tried to keep mum about Trump, and others gave puzzling statements that sought to walk a tightrope between embracing him and distancing themselves from him.

As some conservative commentators lit up social media with images of burning GOP registration cards, some party elders called for a healing process and sought to quiet talk of an independent protest candidacy.

“Life is a series of choices, and this choice looks like one between Donald Trump and Hillary Clinton,” said Haley Barbour, a former Mississippi governor and former national party chairman. “Anybody who proposes a third party is saying, ‘Let’s make sure Clinton wins.’ ”

Senate Majority Leader Mitch McConnell (R-Ky.) stood with Trump, saying, “As the presumptive nominee, he now has the opportunity and the obligation to unite our party around our goals.”

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Trump said he was hardly fretting about whether leading Republicans, such as 2012 presidential nominee Mitt Romney, would eventually back him.

“I believe that the people are going to vote for the person,” Trump said in an interview. “They love their party, but until this year the party was going in the wrong direction. . . . We’ve made the party much bigger.”

Trump spent Wednesday holed up in his soaring New York skyscraper, plotting ways to repair his image and destroy the opponent he calls “Crooked Hillary.” He said he was shellshocked by his sudden emergence as the Republican standard-bearer, having anticipated that his fight with Sen. Ted Cruz and Kasich would continue until June’s California nominating contest. Both left the race in the wake of Trump’s resounding primary win Tuesday in Indiana.

“Who would have thought that I’d be here and we’d be waiting for Hillary?” he said, referring to Clinton being locked in a primary fight with Sen. Bernie Sanders of Vermont.

Kasich, a career politician whose sunny campaign failed to gain traction in a year dominated by anti-establishment anger, suspended his bid Wednesday in Columbus, Ohio, in an emotional speech tinged with wistful anecdotes about town hall meetings he called “absolutely magic.” He said, “The people of our country changed me. The spirit, the essence of America lies in the hearts and souls of us.”