In the brutal 2016 cage-match between Hillary Clinton and Donald Trump, tax returns emerged as something of a broken bottle tossed into the ring. If Hillary could grab it, she'd be able to pull herself off the ropes and lash out with a deadly weapon.
Democrats were sure the returns would show that Trump A: wasn't rich, B: had been colluding with secret ex-Soviet forces, and C: had been dodging his federal responsibilities for something close to 20 years. The hunt was on.
Right down to the electoral wire, Dems were searching frantically for the object of their obsession.