You can’t try a sitting President for any criminal offense. The only criminal proceeding the Constitution allows for a sitting President is the impeachment process.

If impeached, convicted and removed from office then the President could be tried for the underlying criminal offenses related to that impeachment. Article I, Section 3 Clause 7 actually has what amounts to an exception to the double jeopardy clause for this purpose. It explicitly allows a President that has been impeached and removed from office to be held “liable and subject to indictment, trial, and punishment, according to law.”