Paul Ryan
U.S. Speaker of the House Paul Ryan (R-WI) holds a news conference on Capitol Hill in Washington March 17, 2016. Reuters

US Speaker of the House, Paul Ryan has said that he was "not ready" to endorse the presumptive Republican nominee Donald Trump. Ryan, who is the highest-ranking elected Republican and chairman of the Republican National Convention, had previously said he would support the party's eventual nominee.

"I'm just not ready to do that [endorse Trump] at this point. I'm not there right now," Ryan told CNN's Jake Tapper on Thursday 5 May.

Throughout his tenure as speaker, Ryan has made it a point to stand apart from Trump, even going as far as criticising Trump's views, The New York Times noted. In December, after Trump proposed banning Muslims from entering the US, Ryan said the plan was "not who we are as a party" and in violation of the Constitution.

"I think what a lot of Republicans want to see is that we have a standard bearer that bears our standards," the Wisconsin Republican said to CNN. Ryan added he did not want "to underplay what he accomplished" but said he hoped "our nominee aspires to be Lincoln and Reagan-esque—that that person advances the principles of our party and appeals to a wide, vast majority of Americans."

Ryan, who is just the most recent Republican leader to reject Trump, said he hopes to eventually back the billionaire former reality TV star but said he wants Trump to unite "all wings of the Republican Party and the conservative movement". He would also like Trump to run a campaign allowing the American people to "have something that they're proud to support and proud to be a part of."

"And we've got a ways to go from here to there," Ryan said.

The speaker's decision to hold off endorsing Trump comes in contrast to Senate Majority Leader Mitch McConnell, who said he woud support Trump on 4 May. Several high-level Republican figures have opted to forego supporting the last remaining GOP candidate.

Earlier on Thursday, the last two Republican presidents, George HW Bush and George W Bush, announced they would not be endorsing Trump for president. The father-son pair had campaigned earlier in the election for Florida Governor and son and brother, Jeb Bush, who ended his campaign in February. They had previously supported past GOP presidential nominees John McCain in 2008 and Mitt Romney in 2012.

Trump became the party's presumptive nominee earlier after a momentous victory in Indiana, which prompted his last remaining rivals Texas Senator Ted Cruz and Ohio Governor John Kasich to drop out of the race.

Neither Bush president will attend the Republican National Convention in Cleveland in July, CNN noted. McCain and Romney, who chose Ryan as his vice presidential running mate, will also skip the convention.