Donald TrumpDonald John TrumpTrump nominates Jeffrey Rosen to replace Rosenstein at DOJ McCabe says ‘it’s possible’ Trump is a Russian asset McCabe: Trump ‘undermining the role of law enforcement’ MORE Jr.'s emails and meeting with a Russian lawyer during the campaign were a "clear violation of federal law," Rep. Ted Lieu (D-Calif.) said Wednesday. 

Lieu said he believed that Trump Jr. "clearly violated" election law by seeking to get something of value for a foreign national. Election law prohibits candidates from taking money from a foreign source or anything else that might be valuable, such as opposition research.

"Donald Trump Jr. clearly violated the Federal Election Campaign Act by conspiring to solicit something of value from a foreign national," Lieu said on MSNBC's "All In with Chris Hayes."

"And as a former prosecutor, I can tell you that conspiracy is very easy to prove. You just have to show he took an act in furtherance of the crime and in this case not only did he write an email back saying 'I love it,' getting the dirt on Hillary ClintonHillary Diane Rodham ClintonSanders campaign reports raising M in less than a day The Memo: Bernie Sanders’s WH launch sharpens ‘socialist’ question Roger Stone invokes gag order in new fundraiser MORE, he also set up a meeting and showed up at the meeting. That more than completes the crime of conspiracy." 

Trump Jr. on Tuesday released a chain of emails showing how his meeting with Russian lawyer Natalia Veselnitskaya was set up in June 2016.

In one of the emails, Rob Goldstone, a music promoter who arranged the meeting, told Trump Jr. that a chief prosecutor in Russia met with a business associate of then candidate Donald Trump's, and offered "information that would incriminate Hillary" Clinton and her "dealings with Russia."

Goldstone described it as "obviously very high level and sensitive information," and wrote that it "is part of Russia and its government's support for Mr. Trump."

Trump Jr. replied, in part, "if it's what you say I love it."

But Trump Jr. has said that the lawyer offered no damaging information on Clinton during the meeting. 

He has also argued that there was nothing unusual in his meeting with someone offering negative information on a political opponent, though in an interview with Fox News's Sean Hannity he acknowledged that in retrospect, he wishes he had done some things differently.

Political veterans from Republican and Democratic campaigns have said it was unusual to take a meeting with a foreign operative offering information on a rival.

Investigators are probing Russia's involvement in last year's election, including whether Trump's campaign worked with Russia to hurt Clinton's campaign.