Story highlights Ryan faces a primary opponent on Tuesday

Trump declined to endorse Ryan

(CNN) House Speaker Paul Ryan stood by his endorsement of Donald Trump Thursday, but didn't rule out withdrawing it at some point in the future should he deem that necessary.

"None of these things are ever blank checks, that goes with any situation in any kind of race," Ryan said in a radio interview with WTAQ's Jerry Bader in his Wisconsin district.

Ryan added his reason for backing Trump is that "he won the delegates, he won the thing fair and square it's just that simple."

The speaker also shrugged off Trump saying earlier this week he wasn't "there yet" on endorsing Ryan in his upcoming primary next Tuesday.

"The only endorsements I want are those of my own employers in the first congressional district, that's really what my focus is," Ryan said.

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