The remedy to his insurrection on January 6th was impeachment. He was impeached, and his jury found him not guilty. The jury in this case being the United States Senate.
Impeachment is a political process, not a legal process.
EDIT: To back this up, from Wikipedia:
In the United States, impeachment is a remedial rather than penal process,[13][14]: 8 intended to "effectively 'maintain constitutional government' by removing individuals unfit for office";[14]: 8 persons subject to impeachment and removal remain "liable and subject to Indictment, Trial, Judgment and Punishment, according to Law
