Yes, we know how this is going to end. But some developments along the way to President Trump’s acquittal will matter more than others and leave a lasting impact long after the trial ends.The big picture: We’re all going to be flooded with information and distractions over the course of the trial. Here’s what deserves your attention.1) The rules of engagement: It matters how much time House impeachment managers get to present their case, how long Trump’s legal team gets to respond — and what evidence is allowed. Senate Majority Leader Mitch McConnell backed down quickly on his original plan to make House managers and Trump’s team each present 24 hours of arguments over two days. By spreading it over three days each, McConnell may be better able to balance the competing pressures from the White House, which wants a speedy trial, and vulnerable Republicans like Susan Collins of Maine, who pushed for more time.The Senate rules will now also allow evidence from the House impeachment inquiry automatically, though senators can attempt to strike evidence. But Senate Democrats got shut down Tuesday in their early efforts to subpoena White House and State Department documents.All of this will set precedents for future presidential impeachment trials. And don’t kid yourself — there will be others.2) What do we not already know? We’ve learned some new details since the House impeachment vote, such as the Government Accountability Office report that concluded the White House Office of Management and Budget violated the law by withholding military aid to Ukraine.There’s also Lev Parnas’ allegation that Trump knew all about his efforts to pressure Ukraine. But all of that information is already known to the public — so it wouldn’t really break new ground.To advance what's already known about Trump’s actions — not just summarize what's already come out — Democrats would need majority support in the Senate to call witnesses, like former national security adviser John Bolton, or subpoena evidence. We don’t yet know whether either will happen.3) Chief Justice John Roberts’ role: Things likely would have to go pretty far off the rails, even by 2020 standards, for Roberts to end up having much of a substantive impact on the proceedings, Axios’ Sam Baker reports.Roberts has some power to decide evidentiary questions, which could include calling witnesses, but the Senate largely makes its own rules for impeachment trials. And the Senate can overrule Roberts.It wouldn't look great for senators to overrule the chief justice, or be contradicted by the chief justice. But it's also believed that the chief justice himself would prefer to avoid a partisan back-and-forth. (He did scold the House impeachment managers and Trump's legal team early Wednesday morning for their rhetoric.)It’s unlikely Roberts will end up deciding many make-or-break questions; if he does, then the trial will have already taken some unpredictable turns.4) Democrats to watch. Sen. Doug Jones, who’s running for re-election in deep-red Alabama, has written that he wants “a full, fair and complete trial” and has said there are “gaps” in the House case. He’s being targeted during the impeachment trial with a $1 million ad campaign by the pro-Trump group America First Policies.He might not vote to convict Trump if his doubts aren’t satisfied. Two other Democrats to keep an eye on are Sens. Joe Manchin of West Virginia and Kyrsten Sinema of Arizona.There's a well-covered handful of Republicans who could help Democrats force more testimony or evidence — including Collins and Cory Gardner of Colorado, both up for re-election, as well as Mitt Romney of Utah and Lisa Murkowski of Alaska.But any Democratic defections would get an outsized spotlight — especially from the Trump team.5) The Democratic presidential candidates. Every day Bernie Sanders, Elizabeth Warren and Amy Klobuchar aren’t on the campaign trail is a day that they can’t compete with Joe Biden and Pete Buttigieg in chasing votes. The Iowa caucuses are less than two weeks away.Warren and Sanders are both deploying high-profile surrogates to help make their closing arguments this weekend in Iowa — including Alexandria Ocasio-Cortez for Sanders and Jonathan Van Ness, star of Netflix's "Queer Eye," for Warren, Axios’ Alexi McCammond reports.6) What does Trump do? He hasn’t exactly been shy about his comments on the impeachment process — especially on Twitter. Now he has a legal team to fight for him and knock holes in the House impeachment case on his behalf, and a fierce group of media-savvy GOP congressmen to attack his critics on TV.He’s in friendly territory in the Republican-controlled Senate, and the end could come relatively quickly — as long as he doesn’t say anything that causes himself more problems or undermine their work.Editor's note: This story has been updated to include Roberts' scolding of the House impeachment managers and Trump's legal team.