This post is part of Polyarchy , an independent blog produced by the political reform program at New America , a Washington think tank devoted to developing new ideas and new voices.

There’s a ton of speculation right now whether Donald Trump Jr.’s emails are indeed the start of a bona fide Trump-Russia collusion breadcrumb trail. They may indeed be. But as Vox’s Dylan Matthews astutely points out, the facts of the case may not matter as much as what Paul Ryan and Mitch McConnell do with them.

Impeachment, after all, is a political decision. And Ryan and McConnell will decide to let impeachment go forward when the political calculus demands it.

In a recent post, I laid out the costs and benefits Republicans would face in impeaching Trump.

The short version is that letting impeachment go forward will almost certainly damage the Republican Party brand, cost Republicans seats in 2018 and ’20, and prevent them from getting anything done legislatively. It would also provoke a wider civil war within the Republican Party, if Trump fights back and his loyal supporters conclude that he was set up by the “Washington establishment.” These are high costs to pay, and good reasons not to let impeachment go forward.

The benefits to Republicans would be that if they think a spectacular Trump scandal collapse is imminent, it would be better to get out in front of it before the damage gets worse. The sooner Trump is out, the sooner others in the party can work to rebuild it along different lines. Some may also believe that Trump is a genuine danger to the United States and the world, and think the country would be better off with Mike Pence as president.

The big calculus, then, is whether that spectacular Trump scandal collapse is indeed imminent.

If the New York Times has more documents, and access to sources who have additional documents, a steady drip-drip-drip will give this story momentum and make it harder for leading Republican politicians to ignore. But presumably, leading Republicans have already received classified briefings that would give them some inkling of what might be ahead. As John McCain hinted, there are “many more shoes to drop.”

If Republican leaders do decide that the gains from impeaching Trump finally do outweigh the costs, we might not know immediately. Presumably, Senate Republicans will be spending the next few weeks trying to put together a health care bill that can win 51 votes. That’s one reason why, even if this story has momentum, McConnell and Ryan have a strong incentive to stall.

Republican leaders would also need time to build a strong case against Trump so that there’s no doubt. That means giving special counsel Bob Mueller more space to conduct his investigation and the Senate Intelligence more room to conduct its investigation.

At the same time, if they decide they want to go forward, the sooner the better. The longer this gets drawn out, the more damage it does to the party, and the less time Republicans will have to rebuild their brand going forward.

For now, the “these emails are a big deal” voices among the Republicans are the usual Trump critics. John McCain. Lindsey Graham. Susan Collins. Their criticism tells us little.

What will be more telling is if and when other Republicans who have not yet been outspoken start to be. What will be telling is if and when Fox News and Breitbart take this story more seriously. What will be telling is if weeks go by and Ryan and McConnell fail to offer any defense of the Trump administration. Once a cascade begins, it tends to snowball.

If Republicans can’t get their act together to pass the Obamacare repeal bill they’ve promised to pass for going on eight years now, one wonders whether some in the party will start to wonder what the point of having a majority is anyway. If the health care bill fails to come together, and the Trump Jr. email story leads to bigger and more damning stories, the political calculus will begin to change. At that point, a genuine cascade will become more likely.