The White House said Trump called Cindy McCain on Friday to send his best wishes and check on her and her husband.
John McCain was admitted this week to Walter Reed Medical Center due to side effects from his cancer treatment.
The Republican was diagnosed earlier this year with glioblastoma, an aggressive form of brain cancer.
McCain has frequently been a thorn in Trump's side and cast the deciding vote that scuttled Republican efforts to overturn the Affordable Care Act earlier this year.
McCain's office has said he should be able to return to the Senate soon to vote on the GOP tax cut package.
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