Former ethics lawyers for Presidents George W. Bush and Barack Obama Barack Hussein ObamaMomentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina Majority of voters say Trump should not nominate a Supreme Court justice: poll MORE blasted President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE's son in a joint op-ed Tuesday after he admitted to meeting with a Kremlin-linked attorney offering dirt on Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE.

Norman Eisen and Richard Painter wrote in the New York Times that Donald Trump Jr.'s actions raised a slough of new issues for former Trump campaign manager Paul Manafort and senior White House adviser Jared Kushner.

"It raises a host of potential criminal and other legal violations for Donald Jr. and others involved, including his brother-in-law Jared Kushner; Paul Manafort, the campaign chairman at the time; and perhaps the president himself," the two wrote.

"But," the lawyers warned, Trump Jr.'s actions "should not be exaggerated: The investigation has much further to go before Donald Jr.’s liability, or that of others, can be finally assessed."

"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," the former ethics czars wrote.

The lawyers dismissed Trump Jr.'s explanation that the meeting was "nothing" as a "nonsense" excuse.

"The defense that this was a routine meeting to hear about opposition research is nonsense," they wrote. "As ethics lawyers, we have worked on political campaigns for decades and have never heard of an offer like this one."

"If we had, we would have insisted upon immediate notification of the F.B.I., and so would any normal campaign lawyer, official or even senior volunteer."

The ethics lawyers said that the consequences for Trump Jr. and others in the White House could be grave.

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"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," they wrote.

"The promised Russian 'documents and information' would have been an illegal campaign contribution from a foreign government — and a priceless one."

The two concluded by calling for Special Counsel Robert Mueller's investigation into possible collusion between Russia and the Trump campaign to continue uninhibited.

"It is now more critical than ever that the investigations by the special prosecutor and Congress be allowed to complete their course without White House or other interference," they wrote.

On Tuesday, Trump Jr. released emails detailing how an acquaintance, Rob Goldstone, set up a meeting between Trump Jr. and a Russian-linked lawyer who promised incriminating information on Clinton.

Trump Jr. said Tuesday he would be willing to testify under oath about the meeting, and hoped to be transparent about his contacts with Russia.