This time, House Speaker Nancy Pelosi was certain: She publicly accused US President Donald Trump of having violated the constitution. During the past few months Pelosi had warned that reliable evidence was needed to launch impeachment proceedings. But what follows now is effectively Robert Mueller 2.0 — both sides, the Democrats and Republicans, will fight tooth and nail over the "correct" interpretation of the phone call between Trump and Ukrainian President Volodymyr Zelenskiy.

Big gamble for Democrats

This could present a second chance for the Democrats to prove Trump did, in fact, abuse his power. This time, he will not be able to just shrug off the accusation, labeling it a "witch hunt." Trump has told reporters that he did seek dirt on the son of his political rival, Joe Biden. And the memo summarizing Trump's conversation with Zelenskiy clearly shows that the US president asked a foreign leader to launch an investigation into his domestic rival. This constitutes an abuse of power.

But Trump is adamant that there was nothing indecent about his conversation with Zelenskiy. So far, the Democrats' accusations against Trump and those made by Mueller during the Russia investigation have done him no harm. But the Democrats believe that this time things will be different.

One thing is certain: the Democrats are taking a huge gamble. Because once again, just as with the report published by special counsel Mueller, Trump is trying the frame the investigation into his conduct as a desperate attempt by the Democrats to get him out of office. He has already taken to Twitter, proclaiming that impeachment proceedings will merely help him get re-elected.

Read more: Impeachment in the US: How does it work?

Trump's approval rating plummeting

The memo summarizing the phone call makes clear that this time, Trump really did go too far. The impeachment proceedings, meanwhile, will not only take this conversation into account, but also the findings of the Mueller report, which for instance do not rule out that Trump obstructed justice. The proceedings will also garner far greater attention than anything that came before them.  

Currently, however, a majority of US citizens oppose impeachment proceedings. Even so, Trump's approval rating compared to his Democratic rivals is already falling. That's especially true in comparison to Biden, who is leading the polls in the Democratic presidential primary.

It will be impossible for the Democrats to actually remove Trump from office due the Republican majority in the Senate. They would never go along with ousting the president. But even so, the proceedings will hardly help Trump's popularity.

This means we will witness a war of attrition — though one that will benefit the Democrats in the long-term. That's because Trump is wearing down his own popularity: First there was the Mueller report, now we have the Ukraine phone call, and finally there is the looming economic recession.