"Because I have special role as chair of the Republican convention, I stay neutral and I support the nominee," the Wisconsin lawmaker said, explaining that as speaker he will preside over the GOP National Committee this summer in Cleveland.
Ryan added, "All the while I will stand up for what I believe. I will stand up for what I believe is right. I will stand up for our party's principles and our nation's principles."
Earlier this week the speaker strongly denounced Trump's proposed ban on all Muslims from entering the U.S.
"It's not who we are as a party," he said on Tuesday.
But when pressed repeatedly on Thursday to discuss the dynamic inside the Republican Party that has propelled Trump as the clear front-runner, the speaker demurred.
"I weighed in on the comment made in the presidential campaign because I think that needed to be commented on, but I'm not going to spend every day here talking about the go-betweens of what's happening in the presidential race," Ryan told reporters at his weekly press conference on Capitol Hill.
The 2012 vice presidential nominee argued that in the absence of a single national leader it was up to congressional Republicans to lay out a pro-growth agenda and draw a contrast with Democrats in 2016.
And aside from Trump, Ryan made it clear he was moving ahead to create a blueprint for what the GOP should propose to voters in a national campaign.
"I've been on a ticket, I'm familiar with how this works," Ryan, who Mitt Romney tapped as his running mate the last cycle. "I don't think we have time to wait until a nominee arrives, which could be as late, I don't know, June or July, to then come up with an agenda to show the country who we are and what we believe in."