WASHINGTON (AP) — House Speaker Paul Ryan says Republican lawmakers should follow their conscience in deciding whether or not to support Donald Trump, the GOP's presumptive nominee for president.

The Wisconsin Republican told NBC's "Meet the Press" that "the last thing I would do is tell anybody to do something that's contrary to their conscience. Of course I wouldn't do that."

Ryan, who has given a tepid endorsement to Trump, said he understands he is in a "very strange situation" to be supporting the party's presumptive nominee while not urging his fellow lawmakers to follow suit. But he said Trump is "a very unique nominee."

Ryan is the highest elected Republican official and the official chairman of the Republican convention next month. He stunned the political world in May when he held back his endorsement of Trump before grudgingly offering his support earlier this month. Since then, Ryan has been critical of Trump, calling the candidate's complaints about the impartiality of a judge of Mexican heritage a "textbook definition of a racist comment" and reiterating his opposition to Trump's proposal to temporarily ban all foreign Muslims from entering the United States.

As speaker of the House, Ryan said he feels a responsibility not to lead "some chasm in the middle of our party" that would hurt GOP chances to win the White House. His reluctance to embrace the party's nominee wholeheartedly is remarkable for a Republican who was the GOP's vice presidential candidate in 2012.

Ryan was interviewed Thursday for the Sunday talk show. An excerpt was released Friday.

He told reporters at a news conference Thursday that he will continue to speak out in defense of conservative principles, despite a warning from Trump that Republican congressional leaders should "be quiet."

He and other congressional leaders "represent a separate but equal branch of government," Ryan said as he vowed to "robustly defend the separation of powers."

Ryan's comments came as Rep. Fred Upton, R-Mich., a 30-year House veteran and committee chairman, said he will not endorse Trump for president. Maryland's Republican Gov. Larry Hogan also said he will not vote for the billionaire presidential candidate. And Ohio Gov. John Kasich, a former GOP candidate for president, said he's still not ready to endorse Trump.

Ryan said he has no plans to rescind his endorsement of Trump, despite his differences with him.

"I don't have a plan to do that," he said Thursday, calling differences among party leaders "just the way things work."