That is because of the enormous potential legal liability, both individually and for the campaign. The potential offenses committed by Donald Jr., his colleagues and brother-in-law who attended the meeting, and the campaign itself, include criminal or civil violations of campaign finance laws. These laws prohibit accepting anything of value from a foreign government or a foreign national. The promised Russian “documents and information” would have been an illegal campaign contribution from a foreign government — and a priceless one.

Then there is the question of whether the statements of enthusiasm in the emails about the meeting (“I love it,” Donald Jr. wrote) constituted assent on behalf of the Trump campaign to continuing Russian help. Welcoming the information and taking the meeting can reasonably be understood to signal a broader receptivity to Russian aid. This is even more serious than the campaign finance violation because it brings conspiracy law into play. That could make Donald Jr. and others liable for all of the Russian dirty tricks that followed, including any Russian cybercrimes or other crimes targeting the Clinton campaign.

Although we do not yet have enough facts to judge, Donald Jr. and others may also be liable for conspiracy with respect to espionage, depending on how any illicit information was obtained and the level of their awareness of any spying. Because the Russian campaign that followed was nothing less than an assault on our democracy, we understand why some are raising issues of treason as well. Prosecution under the federal treason statute is ultimately unlikely because we are not at war with Russia. But during the Cold War, treasonous conduct was often prosecuted under other statutes. (Alger Hiss was sentenced to four years in prison for “forgetting” in sworn testimony that he had met with Whitaker Chambers, an American working for the Russians.)

Mr. Manafort and Mr. Kushner, who attended the meeting on notice of what was contained in these documents, are also potentially culpable. Mr. Manafort is already reportedly under investigation in connection with Russian contacts; this will add fuel to that fire. Mr. Kushner is very likely being investigated as well for omitting Russian contacts from his security clearance forms. He could be charged with making false statements if it is determined that he intentionally withheld this or other Russia-related meetings from his government filings.

What of Donald Trump himself? Because offers of this kind are the most crimson of red flags in any campaign, they would never normally be undertaken without the agreement of a lawyer, and perhaps the consent of the candidate. That raises the question of whether the president himself knew. There’s a strong possibility he was in Trump Tower when the meeting took place; after all, his office was just one floor away. Would three of his closest confidants really have undertaken this meeting without telling him?