WASHINGTON — The detailed indictment of 13 Russians for intervening in the 2016 presidential election has rekindled a debate that had never fully gone away and now seems destined to become one of the great unresolved questions in American political history: Did Moscow tilt the election to Donald J. Trump?

The 37-page indictment, revealing a sophisticated network that sought to bolster Mr. Trump and undermine Hillary Clinton by staging rallies and purchasing incendiary ads on social media, handed Democrats ammunition to claim that Mr. Trump’s success was illegitimate because it was buttressed by a foreign power.

Yet even as it offered Mrs. Clinton and her advisers some measure of vindication by making clear that the Russians had supported Mr. Trump’s candidacy — an assertion he has long dismissed as a “hoax” — the indictment was also vexing to both Democrats and Republicans.

Opponents of Mr. Trump do not yet have any conclusive proof that he colluded with the Russians. And Mr. Trump’s supporters must continue to contend with questions about whether his upset for the ages was the result of foul play.