Emails released Tuesday by President Trump's son may offer the clearest sign to date of possible criminal violations arising from Russia's meddling in the 2016 election.
Several campaign funding experts say the emails strongly suggest that Donald Trump Jr. violated federal election laws by arranging a high-level campaign meeting with a Russian lawyer who promised to reveal damaging information about Democratic nominee Hillary Clinton.
Federal law makes it a crime for any person to "solicit, accept or receive" a contribution or "anything of value" from a foreign person for a U.S. political campaign or "for the purpose of influencing any election for federal office."
Trump Jr. and his supporters scoff at the notion that having a meeting to learn more about your rival in political campaign would violate federal law, insisting the encounter yielded nothing of value. And even if it had, they say, it wouldn't be the type of money or bribes usually covered under the campaign law.
But others note that the statute includes an "express or implied promise" to give something of value. So in that sense it may not matter whether the thing of value was ever actually provided.
Under the law, those who knowingly and willfully engage in these activities may be subject to fines or imprisonment.
The emails released Tuesday show that Trump Jr. was told that the Russian lawyer could "provide the Trump campaign with some official documents and information that would incriminate Hillary and her dealings with Russia and would be very useful to [his] father. This is obviously very high level and sensitive information but is part of Russia and its government's support for Mr. Trump."
"If it's what you say," he replied, "I love it especially later in the summer." He then set up a meeting at Trump Tower with Paul Manafort, then the Trump campaign manager, and Jared Kushner, the president's son-in-law.
The emails "provide the smoking gun confirming that Donald Trump Jr. illegally solicited a contribution from a foreign national. This is very incriminating evidence," said Paul S. Ryan, a lawyer and vice president at Common Cause, an election watchdog group.
He said giving a campaign opposition research that would damage the rival candidate clearly qualifies as something of value. He said Manafort and Kushner could be charged with an illegal solicitation as well if they understood the purpose of the meeting.
Trump Jr.'s suggestion that he would prefer to see such damaging information appear "later in the summer" could also be seen as a sign of coordination over the timing of the release of the information.
Trump Jr. dismissed such claims, saying that campaigns routinely seek out and accept opposition research about their rivals.
In a sarcastic tweet Sunday, Trump Jr. wrote, "Obviously I'm the first person on a campaign to ever take a meeting to hear info about an opponent."
Some legal experts have questioned whether opposition research would qualify under the law as something "of value," since traditionally the law has been applied to money or gifts rather than information or speech.
"I have a hard time seeing how a meeting is a contribution from a foreign national," said Jan W. Baran, a Washington lawyer and former general counsel for the Republican National Committee. "It's not concrete. It doesn't have a quantifiable value."
Nevertheless, Common Cause filed a complaint Monday with the Federal Election Commission and special counsel Robert S. Mueller III alleging that the recent revelations show the Trump campaign violated the law by "soliciting a contribution from a foreign national."
Election law violations are usually pursued by the FEC as civil matters that can lead to fines and penalties, but the Justice Department sometimes prosecutes knowing and willful violations as crimes.
"There is plenty of evidence this meeting violated the law. He set up the meeting with the Russian lawyer because he thought he would receive something of value for the campaign," said Brendan Fischer, a lawyer at the Campaign Legal Center. "It is also the clearest evidence so far of coordination between the Trump campaign and Russian agents."
When then-FBI Director James B. Comey confirmed in March the investigation into Russia's meddling in the 2016 election, he said there were at least two major questions: Were there "any links" or "any coordination" between the Trump campaign and Russian agents? And second, were any crimes committed?
Critics of the inquiry have argued that there is no federal law that clearly forbids "collusion" between a campaign and a foreign government. But election law uses the word "coordination" and makes it illegal for U.S. candidates to coordinate their efforts with foreign persons.
Randall Eliason, a former federal prosecutor, said that depending on what the investigation reveals, the Trump campaign also could be charged with criminal conspiracy to defraud the United States.
"If Trump officials conspired to help Russians interfere with the election, they could be liable for conspiracy, even if only the Russians did the actual interfering," he wrote last week on the Sidebarsblog.
"Similarly, if Trump officials conspired to help Russians violate bans on foreign involvement in U.S. campaigns, they could be liable for that conspiracy even though they were not foreign nationals and could not have committed the crimes."
But most lawyers predict Mueller's investigation will focus on more narrow and targeted charges, including the possible election law violations.
Kushner and former national security advisor Michael Flynn could also be charged with making false statements if they deliberately omitted from their security clearance forms the fact that they had met with Russian officials. Kushner initially failed to mention the June meeting, but did so later.
And President Trump could face allegations of obstruction of justice for firing the FBI director because Comey had refused the president's suggestion to clear Flynn.
The new reports of contacts between the Trump campaign and Russians may also bolster the obstruction charges, said Harvard law professor Alex Whiting, a former federal prosecutor.
"Despite the old adage that the 'cover-up is always worse than the crime,' obstruction charges will be harder to prove if in fact there were no improprieties to hide," he wrote Tuesday on the Just Security blog.
"That is why the emerging collusion evidence could end up mattering so much to the obstruction inquiry. It has the potential to change everything. Suddenly, Trump's actions to stop the FBI's investigations … feel much more sinister. Now it appears that Trump may have in fact had something much larger to hide."
On Twitter: DavidGSavage
3:30 p.m.: This article was updated with additional background.