Tom Kean Jr. hasn't been seen on Capitol Hill since early March and has told a close circle he's dealing with a medical issue.WASHINGTON – President Donald Trump endorsed Rep. Thomas Kean Jr., a Republican congressman from New Jersey seeking reelection despite mysteriously disappearing from Capitol Hill for three months.Trump said the lawmaker, the son of a former GOP governor of the Garden State, is "working tirelessly" – even though he's missed more than 100 votes in the House of Representatives since early March."HE WILL NEVER LET YOU DOWN!" the president wrote in a June 1 social media post.Kean, who is running for a third term in Congress, is campaigning unopposed in the June 2 GOP primary but faces a competitive general election in November. Long before the absence controversy, the nonpartisan Cook Political Report last year shifted the general election outlook for Kean's district from leaning Republican to a toss-up.Kean has said he's dealing with a medical issue with a positive prognosis, though he hasn't elaborated at all on the specifics of his condition. He has not responded to requests for comment from USA TODAY.Even Speaker Mike Johnson, who remains supportive of Kean, has said the congressman didn't tell him what exactly is going on with his health."He's had a medical issue," Johnson recently told reporters. "I don't even know the details, and I have to respect that."Tracy DiFrancesco Zaikov, a local Republican leader in Somerset County, New Jersey, told USA TODAY in a May 26 email she spoke to him on the phone that week."I feel confident in Tom's ability to move forward and jump into the campaign grind in the coming weeks," she wrote. "While I am not privy to his medical issue, I am sure he will share that information with everyone when he returns. Meanwhile, his office has been operating assisting constituents without skipping a beat."During his disappearance, the congressman has posted occasionally on his campaign and congressional social media accounts. On May 29, he remotely introduced a bill related to federal healthcare coverage for preeclampsia, a pregnancy complication.Zachary Schermele is a congressional reporter for USA TODAY. You can reach him by email at zschermele@usatoday.com. Follow him on X at @ZachSchermele and Bluesky at @zachschermele.bsky.social.