Why have Trump’s poll numbers gone up since the indictment?
I think only Republicans were polled (for the primary election). I don't think these polls were for the general election.
I can report that I was unhappy about the indictment, and hoped for the best for Trump; and only learned (subject to authentication, of course) later of Trump's apparent (subject to comprehensive reviews) lying, keeping docs that weren't his to keep, keeping extraordinarily classified documents that were illegal to keep, and apparently (subject to authentication, of course) giving uncleared folks access.
All just my early impressions, I invite corrections and I'm never defensive about receiving them (although I do ignore impoliteness).