President Donald Trump reacted to the news of Congressman Elijah Cummings passing away by tweeting heartfelt condolences.

The 68-year-old lawmaker passed away on Thursday morning due to “complications concerning longstanding health challenges,” according to a statement from his office.

President Trump tweeted that Cummings’ work and voice will be “very hard, if not impossible, to replace.”

“My warmest condolences to the family and many friends of Congressman Elijah Cummings. I got to see first hand the strength, passion and wisdom of this highly respected political leader,” Trump tweeted. “His work and voice on so many fronts will be very hard, if not impossible, to replace!”

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My warmest condolences to the family and many friends of Congressman Elijah Cummings. I got to see first hand the strength, passion and wisdom of this highly respected political leader. His work and voice on so many fronts will be very hard, if not impossible, to replace! — Donald J. Trump (@realDonaldTrump) October 17, 2019

Cummings, who represented the Baltimore district for over two decades, was an outspoken critic of the president. As the chairman of the House Oversight and Reform Committee, he was one of the lawmakers leading an impeachment inquiry to Trump.

“He worked until his last breath because he believed our democracy was the highest and best expression of our collective humanity,” his wife, Maya Rockeymoore Cummings, said in a statement.

Warm condolences were sent by many from all across the political spectrum following the news.

“There was no stronger advocate and no better friend than Elijah Cummings,” Republican Rep. Mark Meadows said in a statement. “I am heartbroken for his wonderful family and staff—please pray for them. I will miss him dearly.”