Impeachment has stagnated in the polls. That happened with Nixon, too.

This week is arguably the most important to date in the impeachment inquiry into President Donald Trump. It’s the first time there will be public testimony, which comes at a time when the American people have become seemingly locked in their impeachment positions: They’re for the inquiry but much less sold on impeaching and removing Trump from office.

The inquiry has not recently produced major movement toward Americans wanting to impeach the President. Over the last month (the middle of October to the middle of November), 47% of Americans have said they are for impeaching and removing Trump in the average poll. That’s nearly equal to the 44% who are against it. These numbers are the same as an average of polls taken before this point but after the inquiry was announced in late September.

Past impeachment timelines for Bill Clinton and Richard Nixon offer two very different possibilities on where we go from here. From the start, Americans were against impeaching and removing Clinton from office during the 1998-1999 inquiry, and they remained that way.

But the case against Nixon during 1973 and 1974 should give Democrats more optimism. Opinions on impeaching and removing Nixon from office remained stagnant for months on end. Americans were split on the question in Harris polling from January 1974 to April 1974 for Nixon, just like they are now for Trump.

Then the dam started to burst. A combination of factors, including Nixon’s refusal to turn over any more materials in the Watergate case and public hearings during the House impeachment investigation in May 1974, began to change the tide of public opinion.

By the beginning of June 1974, a clear majority were for impeaching and removing Nixon from office in Harris polling.

A look at the recent polling on the impeachment inquiry against Trump (not impeach and remove) does provide reason to believe that the numbers on impeaching and removing him could move.

A majority of just over 50% support the impeachment inquiry in an average of recent polls, while 43% are opposed to it. But before it was announced, a majority of Americans said they were against the inquiry in an August Monmouth poll. Only since late September, when the inquiry was announced, has opinion on it moved toward a majority of Americans being for it.

The public impeachment hearings, therefore, give Democrats an opportunity. What they need to do is convince that small sliver of the public that is for the inquiry but against impeachment to shift toward supporting the impeachment and removal of Trump from office.

If Democrats fail, they could be giving Trump ammunition going into 2020. They’ll be going through with an impeachment that doesn’t have majority support nationally and has even less support in key swing states.