I doubt Mitch first checked with the GOP supreme court justices to see whether they agree.
The “party convicted” in an impeachment is exempt from the double jeopardy protection:
Trump was aquitted in the Senate. If the Republicans on the Supreme Court want to help him a bit, they can point this out. Reading the constitution literally, they will be correct. And from a civil liberties perspective, I do not want to see the double-jeopardy clause diluted.
However, many charges against Trump are different from what he was impeached for. No double jeopardy issue there.