Mitch McConnell is back -- and holding the line on impeachment

He offered no sign of when a trial might begin, pledging instead to move on to other matters: "For now we're content to continue the ordinary business of the Senate."

Pelosi fires back

House Speaker Nancy Pelosi later responded with a direct challenge to members of the Senate, citing Thursday's bombshell report about President Donald Trump's role in withholding security aid to Ukraine -- but did not clarify what her next move will be.

"Leader McConnell is doubling down on his violation of his oath, even after the exposure of new, deeply incriminating documents this week which provide further evidence of what we know: President Trump abused the power of his office for personal, political gain," Pelosi said in a statement. "Every Senator now faces a choice: to be loyal to the President or the Constitution."

Reminder: The House doesn't come back into session until Tuesday. That's the earliest that Democrats could vote to send articles over to the Senate.

What's going on under the surface

CNN's Stephen Collinson writes:

Democrats are seeking to convince Americans that the GOP is cooking the trial to shield an unchained President guilty of committing a dangerous abuse of power -- soliciting foreign interference in a US election.

Republicans, welded inexorably to their norm-busting President owing to his stranglehold on GOP voters, are framing Pelosi's refusal to hand over articles of impeachment as proof Democrats have a weak case no matter how convincing the evidence delivered in testimony by career foreign policy officials.

The showdown reflects how the adversarial grouping of lawmakers and voters into two rival teams threatens Congress' capacity to wield its own constitutional powers in a dispassionate examination of Trump's conduct and whether it is worthy of removal.

The President, who denies all wrongdoing, insisted during his New Year retreat at his Florida resort that he doesn't "really care" if he has a Senate trial or not. But his frenzied two weeks of furious tweets and searing attacks on Democrats tell a story of an agitated commander-in-chief pining for an acquittal that he can portray as vindication and use to vault into election year.

"The Witch Hunt is sputtering badly, but still going on (Ukraine Hoax!," Trump tweeted on Thursday.

Trump also continued to tweet about impeachment on Friday, after ordering a strike that killed top Iranian General Qasem Soleimani and escalating regional tensions.

More impeachment charges?

The House Judiciary and Intelligence committees could bring additional articles of impeachment against Trump, House general counsel Douglas Letter said when asked point-blank by a judge on Friday at the federal appeals court in Washington.

The responses, pushed by Judge Thomas Griffith at the US Court of Appeals for the DC Circuit, illustrate why the House believes the Mueller investigation is still relevant during this era of impeachment.

"There've been two articles of impeachment that have been acted upon. Are you here to say that there may be a third?" asked Griffith, a George W. Bush appointee.

"There might, yeah, absolutely," Letter responded.

"The House Judiciary Committee has not finished its work on impeachment," Griffith offered.

"Nor has the Intelligence Committee," Letter said.

What are we doing here?

The President has invited foreign powers to interfere in the US presidential election. Democrats impeached him for it. A Senate trial is next. It is a crossroads for the American system of government as the President tries to change what's acceptable for US politicians. This newsletter will focus on this consequential moment in US history.

Keep track of the action with CNN's Impeachment Tracker. See a timeline of events. And get your full refresher on who's who in this drama.