I felt the same way in 1970 when Harry Blackmun was confirmed by a vote of 94-0 when President Nixon nominated him to the Supreme Court. Nixon's previous nominees, Southern conservatives, had been voted down by the Senate, so when Blackmun sailed through, I was suspicious. Our suspicions about Blackmun were confirmed when he wrote Roe v. Wade.
Mattis should never have agreed to work for Trump. He’s old enough to turn it over to someone else. To think that he would stick around with this result suggests an ulterior motive.