U.S. President Barack Obama warned on Friday that occupying the Oval Office “is not a reality show,” in a cutting remark to outspoken Republican candidate Donald Trump who is vying to replace him in the White House.

A fight with Obama would add up to the billionaire’s delight in responding to attacks from rivals and lashing out at his opponents to, surprisingly, gain more support.

Asked about Trump at a media briefing in the White House, Obama called on the press and public to weigh past statements by the Republican but did not point to any specific issues or remarks.

“This is not entertainment,” Obama said, a reference to Trump’s television background. “This is not a reality show. This is a contest for the presidency of the United States,” he said.

Some top Republican leaders – U.S. House Speaker Paul Ryan among them – are still expressing wariness about Trump, who became the party’s presumptive nominee this week when two Republican rivals dropped out of the White House race.

Former Florida Governor Jeb Bush, who ran unsuccessfully for the Republican nomination, posted on Facebook that he will not vote for Trump – one of the sharpest slights yet against the New York real estate mogul by a senior Republican.

“Donald Trump has not demonstrated that temperament or strength of character. He has not displayed a respect for the Constitution. And, he is not a consistent conservative. These are all reasons why I cannot support his candidacy,” Bush wrote, adding that he would not vote for likely Democratic nominee Hillary Clinton either.

U.S. Senator Lindsey Graham from South Carolina, who made an unsuccessful bid for president, joined a growing list of Republicans who are refusing to support Trump and he announced on Friday he will also skip the Republican convention in July. Mitt Romney, who won the Republican nomination in 2012, is also refusing to support Trump.

But Trump on Friday won the endorsement of another former Republican presidential nominee, Bob Dole, who lost to Bill Clinton in 1996.

Trump shrugged off the high-profile Republicans refusing to vote for him, as he said that such GOP naysayers wouldn’t really matter when compared to all the votes he had garnered in primary elections.

Appearing at rallies Friday in Nebraska and then Oregon, Trump repeated his nickname for Democratic front-runner Hillary Clinton — “crooked Hillary” — but stepped up his attacks on Clinton by referencing her husband’s infidelities for the first time since he became his party’s presumptive nominee while dismissing her criticism of how he treated women.

“Bill Clinton was the worst in history and I have to listen to her talking about it?” Trump said. “Just remember this: She was an unbelievably nasty, mean enabler. And what she did to a lot of those women is disgraceful. So put that in her bonnet and let’s see what happens.”

Trump also turned to a relatively fresh target, Sen. Elizabeth Warren. The Massachusetts Democrat, he said, is a “goofus” and a “basket case” who has done nothing in the Senate. Warren, a favorite of the Democratic left whom some would like to see as Clinton’s running mate, had insulted Trump earlier on Twitter, calling him “a bully who has a single play in his playbook.”

Vilifying Democrats was to be expected, but Trump’s problems within the GOP itself remained an unusual spectacle of Republican vs. Republican discord. The nominee-to-be reluctantly agreed to meet next week with House Speaker Paul Ryan, the nation’s highest-ranking Republican whose statement a day earlier — he said he was not ready to embrace Trump’s nomination — set off the intraparty fireworks. Trump said he had “no idea” if they would patch things up.

“The thing that matters most are the millions of people that have come out to vote for me and give me a landslide victory in almost every state,” Trump said moments after Ryan announced their planned meeting.

Rather than let the subject rest, Trump told supporters Friday night in Eugene, Oregon, that he and Ryan had had a nice phone conversation three weeks ago but that, “all of a sudden, he wants to be cute.” Still, Trump assured the thousands gathered that “we’re going to be a unified party.”

Ryan said his meeting with Trump would take place next Thursday and that Trump also would meet with other congressional leaders on Capitol Hill. Discussions will center on “the kind of Republican principles and ideas that can win the support of the American people this November,” Ryan said.