Democrats have an impeachment momentum problem

To understand where the impeachment inquiry has gone so far, and where it's likely to go next, you need to keep in mind one key concept. Hint: it's not quid pro quo.

It's momentum.

To date, House Democrats have built on the original whistle-blower's document by eliciting behind-closed-doors depositions from those officials in the State Department, Defense Department, and White House who are willing to defy Donald Trump's order not to participate. By leaking the headlines of their testimony, the Democrats have been able to dominate the news cycle for weeks.

The polls seem to indicate that the public is listening, at least to some extent: since the formal inquiry was launched, the percent of people who support impeachment has risen from 39% to 49%. Impeachment supporters now narrowly outnumber impeachment opposers.

Yet the Democrats are reaching the end of this phase of quasi-secret investigative depositions. And public hearings will pose a significant challenge to the Democrats' momentum.

The first problem the Democrats will face is that much of the public — and all of the media — already knows the basic outlines of the story that will unfold in the public testimony. That's because of the basic fact that the Ukraine scandal is fairly simple: Trump pressured the president of Ukraine to investigate a political rival, and he conditioned military aid and a White House visit on a public announcement that such an investigation would take place.

As Nancy Pelosi and other Democratic leaders noted at the beginning of the impeachment inquiry, the simplicity of the narrative is a major virtue from their standpoint. The public neither wants nor would tolerate anything with the complexity of the Robert Mueller investigation.

Sure, scandal aficionados can nerd out over the details of which Ukrainian prosecutor is connected to what network of Ukrainian oligarchs. And there's always some pleasure to be taken in observing just how remarkable are the public-service resumes of the so-called deep-state witnesses, like Ambassador William Taylor, who have testified against Trump. However, these will not sustain more than a single news cycle.

The one significant twist still remaining in the current phase of desposition-taking will come when former national security adviser John Bolton either comes forward or definitively bows out.

The arch-hawk is not much liked by Democrats, but neither were his fellow former George W. Bush administration officials pleased when he went to work for Trump. Nevertheless, Bolton is a patriot by his own lights. There has already been testimony that he referred to the alternative Ukraine policy being cooked up by White House acting Chief of Staff Mick Mulvaney and others as a "drug deal" that he wanted no part of. It's therefore conceivable that Bolton would be able to testify directly about the quid pro quo. It's also conceivable, however, that some of the knowledge he has might be subject to executive privilege. And Bolton is likely to take seriously the consequences of any testimony for the office of the national security adviser and for the presidency. The result could be either dramatic testimony or a dramatic refusal to testify.

Once the Bolton issue is resolved, the move to public testimony will be unavoidable. That stage will give rise to the second major challenge to the Democrats' momentum: the Republican counterpunch in the form of a concerted attack on the very rival Trump asked Ukraine to investigate: Joe Biden. Once television cameras are in the room, Republican members of Congress can be expected to use their equal questioning time to hammer home Trump's allegation that Joe and Hunter Biden did something corrupt.

The Democrats (not to mention the Bidens) are potentially vulnerable to this method of momentum-breaking. Although Biden has insisted that neither he nor his son did anything wrong, the reality is that Hunter Biden took a position on the Board of Directors of Burisma, a Ukrainian energy company controlled by an oligarch who was under investigation for money-laundering by Ukrainian prosecutors. Joe Biden, as vice president, sought the removal of the investigation's chief prosecutor. Although Joe Biden's actions were consistent with U.S. policy — American and IMF officials were frustrated with the prosecutor for not taking a stronger stance against corruption, and indeed, it seems that despite being assigned the Burisma case he basically ignored it — the basic sequence of events creates an appearance of impropriety.

The Democrats don't have a simple response to this, except to insist on their narrative and hope the public won't be distracted. To maintain momentum in the public hearings stage, they will have to try a "greatest hits" strategy, getting the existing witnesses in front of the public for brief and pointed hearings.

Although momentum has been on the side of Democrats so far, many things can still change that. The path forward will have more twists and turns.