I am not a lawyer. That said, a case can be made that any jury in DC is prejudiced against Republicans and Trump by virtue of polls, election results and media coverage. We are still guaranteed a jury of our peers. At the very least, juries need to be composed of a cross-section of the national electorate.
This may all be moot, actually. I believe Presidents cannot be tried in civilian court while serving. The only allowable Constitutional venue is Congress and they need super majorities to impeach and convict on very explicit, specific grounds, which have not been met.
A jury of your peers means a cross section of the citizen population, randomly drawn, from the the relevant jurisdiction (here, the District of Columbia), not the entire country.
I don’t know about a trial in a civilian court. Maybe impeachment is the only remedy, in which the “trial” would be in the Senate, although he probably could be tried after he leaves office in court. I don’t think a Senate trial would place him in “jeopardy” for the purposes of double jeopardy.