WASHINGTON - Sam Clovis, a top adviser to President Donald Trump during his election campaign, on Thursday withdrew his candidacy for a senior administration post, just days after he was linked to another aide who pleaded guilty in the probe into alleged Russian meddling in the 2016 election.In a letter to Trump describing his decision, Clovis made no mention of the Russia controversy, but cited "the political climate inside Washington.""The relentless assaults on you and your team seem to be a blood sport that only increases in intensity each day," Clovis wrote in the letter, dated Wednesday. "As I am focused on your success and the success of this Administration, I do not want to be a distraction or negative influence."Trump had nominated Clovis, his 2016 campaign's national co-chairman, to a top post as chief scientist at the Department of Agriculture.A source familiar with Special Counsel Robert Mueller's investigation identified Clovis as the unnamed campaign supervisor in a court filing who had discussions with former Trump foreign policy adviser George Papadapoulos about efforts to improve US-Russian relations and setting up meetings between senior Trump campaign and Russian officials.Papadapoulos pleaded guilty earlier this month to lying to Federal Bureau of Investigation agents about his dealings with Russians."Mr. Clovis’s nomination was only withdrawn because that would certainly have been a topic during his upcoming testimony, under oath, before the Senate Agriculture Committee," Democratic Sen. Patrick Leahy, a member of the committee, said. "I know because I was going ask him all about it to get more facts on the record and before the American people."