Senate Majority Leader Mitch McConnell is preparing for the first impeachment trial of a president in two decades. There are plenty of details to work out, but the overarching structure will likely be familiar. A group of House lawmakers will first present the articles of impeachment to 100 senators and lay out their case for convicting President Donald Trump. Trump’s lawyers will then present their arguments for his acquittal. The senators will deliberate over the evidence, and then they will cast their votes.

Trump knows he’s losing this battle. He green-lit a thuggish stunt by House Republicans to physically disrupt closed-door depositions on Wednesday. He also reportedly lashed out at Senate Republicans for not doing more to protect him, demanding hearings in his favor and more forceful defenses from GOP lawmakers in public. At the same time, he’s failed to provide them with a cogent defense of his actions that can be easily relayed to their constituents. All of this raises a very simple question for Senate Republicans: What, exactly, is the case for acquitting him?

Trump is already losing the case on the merits. The White House’s own memo of his July 25 call with Ukrainian President Volodymyr Zelenskiy proves that Trump asked a foreign government to undermine his political opponents for personal gain. As I’ve noted before, this is an impeachable offense in and of itself. Trump’s defenders have argued that he wanted to tackle corruption in Ukraine writ large, but the president only focused on cases that would falsely tar Biden and Hillary Clinton. Trump also fatally undercut that point by publicly urging Ukraine and China to open anti-corruption investigations into Biden on the White House lawn last month.

Many GOP lawmakers defended Trump in the inquiry’s early days by arguing that there was no quid pro quo. This talking point crumbles with each passing day.

Many GOP lawmakers defended Trump in the inquiry’s early days by arguing that there was no quid pro quo. This talking point crumbles with each passing day. Gordon Sondland, the U.S. ambassador to the EU, testified last week Trump told him in May to speak to Rudy Giuliani, the president’s legal fixer, about corruption in Ukraine before agreeing to a White House visit for Zelenskiy. Giuliani then told Sondland that same day that he wanted a public statement from Ukrainian officials on a mythical DNC server and the Burisma case—that is to say, a Clinton investigation and a Biden investigation. In order for Zelenskiy to earn the prestige and access that comes with a personal White House visit, he first had to prove himself to President Trump by undermining his domestic political rivals. (See also: Quid pro quo.)

More damaging evidence came on Tuesday from Bill Taylor, who currently serves as the highest-ranking U.S. diplomat in Ukraine. His 15-page opening statement depicts a career civil servant trying to uncover and contain the fallout from a shadow foreign policy run by Giuliani, Sondland, and other close Trump associates. Taylor testified that Sondland told him in September that U.S. military aid and a White House visit for Zelenskiy would be “dependent on a public announcement of investigations” by Ukrainian officials. (Once more: Quid pro quo.) “[Sondland] said that President Trump wanted President Zelenskiy ‘in a public box’ by making a public statement about ordering such investigations,” Taylor told lawmakers.