CLEVELAND— On Monday, House Speaker Paul Ryan acknowledged presumptive Republican nominee Donald Trump was “not my kind of conservative” but called for the Republican Party to rally behind Trump at this week’s Republican National Convention.

Speaking at a lunch hosted by The Wall Street Journal Ryan said that while he Trump differ on certain policy proposals such as building a wall on the U.S.’s border with Mexico, or their stances on Muslims entering the country, they are both “on the same page” when it comes to the party’s core principles. “We’re a big tent party. Big tent—real big,” he said.

Paul Ryan endorsed trump last month, after initially declining to do so, but has kept his distance from the presumptive nominee. At times he has even criticized Trump for some of his controversial comments.

On Monday, Mr. Ryan offered a clear reason for why he had ultimately decided to endorse the candidate. “What I do know for sure is if we disunify, then we hand the left the country by default for another four years,” he said. “I just don’t want to be a party to that. I don’t want to be complicit to that.”

Ryan called for the party to display its unity at this week’s convention, acknowledging that many Republicans—who he said were in “wait-and-see mode”—have been reluctant to rally behind Mr. Trump in recent months. He called Mr. Trump’s choice of Indiana Gov. Mike Pence as his running mate a “good signal-sender” and said it “helps tremendously” to unite the party.

Ryan has characterized his relationship with Mr. Trump as “very frank,” saying, “There are things I take issue with that I want to make sure it’s clear why I do.” He added: “He does listen.”

While drawing a contrast between his and Mr. Trump’s approaches, Mr. Ryan said there was no question that Trump deserves to win the party’s nomination, and he praised Mr. Trump’s ability to appeal to a different set of voters.

When Ryan was asked about a recent Trump rally in Wisconsin where attendees booed the candidate’s mention of Ryan, the speaker said that incident illustrated positivity in regards to Trump drawing new voters into the Republican Party.

Ryan noted Trump’s popularity among union voters in, who he said feel “disaffected by the progressives” but not drawn to conservatives, either. “They see Donald Trump as sort of a port in the storm. That’s the upside he brings to the party.”

On Monday former New York Major Rudy Giuliani went all out for Trump during his speech at the convention. Will Ryan be able to do the same tonight?