Special counsel Robert Mueller’s probe is yielding indictments and charges at a fast pace, implicating several aides on President Trump’s 2016 campaign. And some legal scholars argue that the president has impeded the investigation into allegations of collusion between the campaign and Russian officials in a way that reaches the threshold of obstructing justice. Still, at the moment, the impeachment of Trump seems far-fetched. For one, Mueller hasn’t accused Trump of anything. Secondly, Republicans control Congress, which has the formal power to impeach and remove a president. And Trump’s party has largely dismissed any suggestion that the president has done something wrong, either during the campaign or since he took office.

But here’s the thing: The conditions are developing for the U.S. House to be considering Trump’s impeachment less than a year from now, even as Democratic Party leaders are actively trying to downplay this possibility. There are four things that clearly would have to happen for the groundwork for Trump’s impeachment to be set. All four are plausible, but none is guaranteed. And two will largely be determined by this fall’s elections.

Keep in mind that we are talking about impeachment, not Trump’s removal from office. Impeachment, which is the equivalent of being indicted, requires a simple majority vote in the House; for a president to be removed from office, two-thirds of the Senate has to vote to do so after holding a trial. That high Senate threshold makes Trump’s ouster much less likely than his impeachment.

Here are the four steps that would put Trump on the path to impeachment:

1. Democrats win control of the House in November

This is the big, obvious factor.

Impeachment in modern times has largely been a partisan process. The House Judiciary Committee’s votes on articles of impeachment against Richard Nixon in 1974 and the vote in the full House against Bill Clinton in 1998 largely fell along party lines. Nixon resigned before the full House, then controlled by the Democrats, could vote to impeach him. About 25 years later, a House in Republican hands successfully pushed through two articles of impeachment against Clinton, over the objections of most congressional Democrats.

That pattern of partisanship is continuing in the Trump era. House Republicans are largely defending Trump. In contrast, House Democrats are already suggesting openness to impeachment. U.S. Rep. Al Green, a Democrat who represents a Houston-area district, introduced resolutions in December and January that call for Trump’s impeachment on account of his “high misdemeanors,” arguing that Trump’s conduct, such as his controversial remarks last summer in the wake of a white nationalist rally in Charlottesville, is unbecoming of a president. The January resolution got slightly more support than the December one, with about a third (66 of 193) of House Democrats taking the pro-impeachment position. No Republican did.

So for the House to consider impeachment, a Democratic majority is probably necessary. And the Democrats have a strong chance of winning the House this fall. The incumbent president’s party usually struggles in midterm elections, and that effect could be even more pronounced because of Trump’s high unpopularity and what appears to be a very energized Democratic base.

2. A pro-impeachment majority takes control of the House Democratic caucus

This is probably the most complicated of these four steps toward impeachment. It shouldn’t be assumed that a House controlled by Democrats would conduct an impeachment process. Rather than trying to end Trump’s presidency through a process that is likely to divide the county and could anger swing voters, congressional Democrats could use their new majority power to weaken Trump in other ways, including by blocking his legislative agenda, in an effort to ease the path to victory for the Democrats’ 2020 presidential nominee.

I can imagine House minority leader Nancy Pelosi, who was leading the Democrats well before the so-called resistance emerged, advising a Democrat-controlled House against going the impeachment route. She voted against both of the Green-sponsored measures and has spoken out against pushing for impeachment if Democrats win control of the House. Also, Democrats who win seats in November in districts previously held by Republicans might want the party to take a more cautious course. By definition, they don’t hail from liberal strongholds; otherwise, their districts would already have a Democratic representative.

Democratic Rep. Jerry Nadler of New York is the top Democrat on the House Judiciary Committee (where impeachment processes have started in the past) and has said publicly that Democrats should not push for impeachment unless that effort will get some Republican support. Nadler argued that an impeachment in the House that is guaranteed to fail to get the two-thirds required in the Senate for removal serves little purpose. And since it’s very unlikely that Democrats will have 67 Senate seats anytime soon (the party controls 49 right now), that means many GOP senators would need to back Trump’s removal along with Democrats.

But I don’t think Nadler’s and Pelosi’s current reluctance about impeachment is necessarily a great predictor of how House Democrats overall will view the issue at this time next year. The number of House Democrats in favor of impeachment could grow. I think it will.

Why?

First, current Democratic members of Congress could be pushed by their constituents to adopt the pro-impeachment position. Democrats hate Trump, who has a 9 percent approval rating among them, according to Gallup. A recent NBC News/Wall Street Journal poll found that 70 percent of Democrats want the House to hold impeachment hearings.

Trump is showing few signs that he’ll start appealing to Democrats, and his conduct amid the Russia investigation (such as sharply criticizing the FBI and Justice Department for continuing the probe) is likely to reinforce the feeling among Democrats that he is impeding the investigation. Also, California businessman Tom Steyer is funding a national campaign of television commercials calling for Trump’s impeachment (reportedly over Pelosi’s objections), which could move liberal-leaning voters to urge their members of Congress to push for Trump’s ouster.

And by early 2019, there will likely be numerous Democratic presidential candidates in Iowa and New Hampshire whipping up even more anti-Trump sentiment among party activists.

Secondly, if Democrats win a majority in November, there will be new members coming to Congress. Most congressional primaries have not happened yet, but it will be worth watching how many of the Democrats who win the primary in districts currently held by Republicans back impeachment.

The number I’m watching for is 150. Taking back the House means that Democrats will have at least 218 seats. And if the number of Democrats in favor of impeachment proceedings grows from the 66 who supported Green’s second measure to 150 over the next year, that would give the pro-impeachment group a clear two-thirds majority of the party’s House members. I’m not sure that Nadler or Pelosi can stop an impeachment push if it has that kind of backing. In that case, I expect that the vast majority of Democrats would fall in line and back impeachment rather than irritate liberals back home — likely resulting in enough pro-impeachment sentiment to impeach Trump.

I’m suggesting that the Democratic Party is showing signs of being more like the Republican Party, with its more pragmatic leaders being pushed to take more controversial stands by a fiery base. Democratic leaders kind of stumbled into a government shutdown over immigration policy in January after party activists made a very aggressive case that defending young undocumented immigrants was a moral imperative for the party and congressional leaders didn’t make a strong anti-shutdown case. Will Pelosi really be able to convince Democratic activists to look to the 2020 elections to stop Trump when they see him as an immediate danger? I doubt it.

3. A pro-impeachment speaker leads the Democrats

The speaker, as the leader of his or her party in the House, usually also has informal power to shape that party’s strategy. I tend to assume that if a clear majority of House Democrats supported impeachment, the new Democratic speaker wouldn’t stand in their way. But it’s still something of a question mark — with the answer determining whether the impeachment process could go forward.

Pelosi is theoretically first in line for the job if Democrats win the House. But she is a fairly controversial figure among House Democrats, some of whom think she has stayed too long at the helm (she has led House Democrats since 2003). So there’s no guarantee that she will return to the speakership if Democrats win the majority. If the Democrats have sufficiently embraced a pro-impeachment position (see No. 2), adopting it could be a condition for Pelosi — or whoever challenges her — to take the gavel.

4. The party finds and agrees on impeachable offenses against Trump

You might think this should be No. 1 on my sequential list, but I think I’m correct in listing it here. In many ways, an impeachment offense is whatever a majority of House members thinks it is. In Clinton’s case (perjury, obstruction of justice), Congress made a legal (rather than a moral or political case) against the president. In Trump’s case, Democrats are talking about three general charges, two of which take that legalistic approach:

A: “High misdemeanors”: The impeachment resolutions pushed by Green were basically a list of Trump actions that the Texas representative considers egregious acts by an American president, including Trump’s remarks after Charlottesville; his reported reference to “shithole” countries whose residents he did not want to immigrate to the United States; and his criticism of NFL players who refused to stand during the national anthem to protest racial inequality in the U.S.

I suspect that some Democrats would be uncomfortable pushing this type of impeachment resolution, because it’s essentially a case against Trump’s political style, as opposed to one accusing him of formal legal violations. It could risk leading to a political tit for tat, leaving future Democratic presidents vulnerable to impeachment on similar grounds.

B: Obstruction of justice: A group of six House Democrats, including Green and led by Memphis-area Rep. Steve Cohen, has separately written an impeachment resolution arguing that Trump’s conduct around the Russia investigation, particularly his firing of FBI Director James Comey, is evidence of obstruction of justice.

The findings of Mueller’s investigation obviously could have a major impact on the impeachment conversation and efforts, particularly with regard to obstruction of justice allegations against Trump. If Mueller publicly declared that Trump had not obstructed justice, that would not bar House Democrats from reaching the opposite conclusion — but it would surely make doing so more politically fraught. Alternatively, if Mueller concluded that Trump did obstruct justice but opted to defer to Congress on whether to issue an indictment, that would make it easier for House Democrats to more forward with impeachment proceedings. And if Trump agreed to speak to Mueller and committed perjury in the process, that testimony could become the basis for impeachment.

C: Emoluments: The Cohen resolution also argues that Trump is violating the Constitution’s “emoluments clause” forbidding a U.S. president from taking money from foreign governments. The resolution argues that officials from foreign governments are staying at the Trump International Hotel in Washington to, in effect, funnel money to Trump.

I’m not suggesting that Democrats should seek to impeach Trump. And I’m not sure how likely it is to happen. So much could change in the next year, particularly with Mueller’s investigation. And, again, impeachment is not removal. Clinton was impeached and two years later, as he was leaving office, had an approval rating in the 60s.

But the combination of liberal antipathy for Trump, the guilty pleas from his former campaign advisers, the public discussion about whether Trump obstructed justice, the Steyer commercials and the Green and Cohen resolutions make the impeachment of the president a much more realistic possibility than it was during the administrations of George W. Bush or Barack Obama. And it will become an ever more real prospect if Democrats win control of the House this fall.