For nearly a month Americans have been waiting.
It’s been a phoney war.
The calm before the combat.
The House of Representatives impeached the President before Christmas.
But then in a surprise tactical twist the House Speaker, Nancy Pelosi, refused to pass on the two Articles of Impeachment to the Senate.
It meant the Senate trial of President Trump could not begin.
Finally, that log-jam is about to end.
On Wednesday, the House will vote to send the impeachment process to the US Senate.
At that point, for only the third time in American history, the Senate trial of a US President will be underway.
House Democrats will also today appoint “managers” of the trial - they will act as prosecutors.
The White House will appoint the President’s defence lawyers.
None of this will be lightening quick.
There will be several days of technical procedures and backroom negotiations before the trial gets underway in any meaningful sense.
First, the Chief Justice of the Supreme Court must be sworn in - they will run proceedings.
In turn, they will swear in the 100 Senators to serve as jurors.
But then comes the big question.
Will there be additional witnesses?
That could prove fateful for the outcome.
That’s because there is a wildcard out there.
The name of that wildcard is John Bolton, Trump’s former National Security Adviser.
He has made clear that if asked he would agree to testify before the Senate.
But what secrets does he hold against the President...and will he spill them?
Bolton is one of the canniest and savviest bureaucratic operators in all of Washington.
He knows the system better than anyone, and - remember - he called the rogue White House operation in Ukraine a “drug deal".
When he was fired from his job last year, surely he was smart enough to leave with damning evidence against his political enemies.
We don’t know how damaging Bolton might be to Trump.
But all Democrats - and a handful of Republicans - are keen to find out.
That’s why the question of witnesses is such a high-stakes issue.
The long-standing assumption is that President Trump will not be convicted (it would require a two-thirds majority), but then those same experts assumed he would never win the presidency in the first place.
That’s why the Senate trial of a President is the greatest political drama that America has to offer.
And when you’ve a reality TV president who embraces the unpredictable and key insiders like Bolton aching for revenge... well, watch this space.