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Democrats’ third and final day of opening arguments was focused on the second impeachment article the House passed against President Trump: obstructing Congress. And they had strong words about what they said Trump did to obstruct them.

“He is a dictator,” House impeachment manager Rep. Jerrold Nadler (D-N.Y.) said of Trump. “This must not stand.”

Let’s review what obstruction of Congress means and why Democrats really think Trump should be removed from office for it.

What the obstruction of Congress charge is about

Democrats say that Trump blocked Congress’s investigation into his alleged wrongdoing, wholesale. And that is true. A few weeks into the impeachment inquiry, the White House sent a fiery letter to Democrats saying it wouldn’t cooperate with the inquiry, arguing executive privilege. It banned key players from testifying — most notably acting chief of staff Mick Mulvaney and former national security adviser John Bolton — and others from providing documents.

Every Trump administration official who testified did so in violation of the ban.

Why House Democrats think Trump should be removed from office for this

Trump defied all of their subpoenas for people and documents in this inquiry. A subpoena is Congress’s legally binding tool to make people talk who don’t want to. Congress’s rules say that ignoring it is punishable by “a substantial fine” and imprisonment for up to one year.

Why should Republicans care that Trump ignored House Democrats’ subpoenas? Well, Democrats argued that what Trump did is a direct affront to them as well. That this isn’t about Democrats vs. Trump, it’s about Congress vs. the executive branch and Congress’s constitutional right to hold the president accountable. They pointed out that even President Richard M. Nixon let his senior officials testify as he was about to be impeached on a charge of obstruction of Congress for not complying with subpoenas.

Democrats also tried some what-about-ism to woo Republicans: “Just imagine how [House Republicans] would have reacted if President Obama had ordered total defiance of all subpoenas,” Nadler said. “There would have been outrage. Why? Because Congress unquestionably has the authority to investigate presidential conduct.”

There’s no doubt about it, legal and constitutional experts have said: Trump is steamrolling Congress’s power to hold the executive branch accountable. But Republicans have been largely willing to acquiesce to Trump’s expansive definition of presidential power. Their constituents demand loyalty to Trump, so they have no choice but to give up some of their collective power as members of the legislative branch to ensure staying in power themselves.

The political fights over things happening outside the Senate floor

During breaks in the trial, senators often walk over to reporters and stir up drama because, well, they’re politicians. Here are four political fights about the trial brewing behind the scenes.

1. How long Democrats are taking to make their case: They had 24 hours under the rules, and they took most of it. Senators signed up for this by being senators, but for any human being, sitting for nine or 10 hours a day, six days a week, without a phone, is draining. Could Democrats’ lengthy case risk alienating the Senate Republicans they need to vote next week to extend the trial and call witnesses? Already some Republican senators are using the length of Democrats’ presentation to say it wasn’t effective.

“Old expression: Very few souls are saved after the first 20 minutes of a sermon,” Sen. John Neely Kennedy (R-La.) said on Friday.

2. Lt. Col. Alexander Vindman: He is one of the Democrats’ star witnesses, having listened to Trump’s July 25 call with Ukraine’s president and defying the White House ban to testify about it. Also, Vindman still works at the White House. But there is a movement in conservative circles to smear Vindman, an Iraq War veteran, as unpatriotic. This week, one of those allegations that The Fix’s Aaron Blake explains here got elevated by a sitting U.S. senator, Marsha Blackburn of Tennessee, and shared by Trump on Twitter. It goes to show how far Republicans will reach to undermine evidence against Trump.

3. More evidence that Trump saw former ambassador Marie Yovanovitch as a threat: He told Ukraine’s president “she’s going to go through some things.” A Republican lobbyist boasted he was having her followed, though he now says he said that in jest. And now it appears that Trump told people to “take her out,” according to a recording of him reported on by ABC News. Yovanovitch was removed by Trump this spring from Ukraine. The mystery of her ouster grows.

4. Whether to bring in the Bidens: Democrats talked at length Thursday about why Trump was out of line to allege wrongdoing in Ukraine on the part of former vice president Joe Biden. But rather than case closed, Trump’s defenders in the Senate seized that as an opening to talk about Trump’s political opponent. They argued that by even mentioning the Biden family in the trial, Democrats raised the question of whether there was a there there when Biden told Ukraine to fire its top prosecutor as his son had lucrative business dealings in Ukraine.

“Nobody has done an investigation anywhere near like the Mueller investigation of the Bidens, and I think they should,” Sen. Lindsey O. Graham (R-S.C.) told reporters Friday.

Fact check: There is no evidence Biden acted corruptly on the Ukraine matter, as Trump alleges, even though he and his son have said the appearance wasn’t good. And it’s likely that Trump’s defense would have brought up the Bidens anyway, because Trump does a lot.

But that Biden is a thing speaks to how difficult Democrats’ job is compared with Republicans in this impeachment trial. Democrats had to spend three long days laying out all their evidence against Trump. And toward the end, Republicans can just say “Bidens” and immediately inject confusion into this impeachment process about who is being investigated.

Adam Schiff’s last line

Lead impeachment manager Adam B. Schiff (D-Calif.) spent more than an hour Friday night closing up the Democrats’ case. He mentioned Trump’s lawyers by name and pre-butted arguments we expect them to make. Some lines that stood out:

On senators being bored: “Are the blessings of freedom so meager that we will not endure the fatigue of a real trial with witnesses and documents?”

On Trump’s defenders bringing up Biden: “What they hope to achieve in a Senate trial is what they couldn’t achieve in this scheme.”

On Trump decrying how Schiff paraphrased his phone call: “For a man who loves to mock others, he does not like to be mocked.”

On American democracy writ large: “I believe this may be one of those moments, a moment we never thought we would see, a moment when our democracy was gravely threatened and not from without, but from within.”

What’s next?

Trump’s defense team begins its opening arguments Saturday at 10 a.m. Eastern. Tune into The Washington Post’s live show at 9:30 a.m., where I’ll be analyzing the day ahead.