WASHINGTON – President Trump on Thursday defended his son's meeting with a Russian lawyer whom he believed had political dirt on Hillary Clinton – calling it a normal practice during a U.S. presidential campaign.

"It's called opposition research, or even research into your opponent," Trump said at a joint news conference with French President Emmanuel Macron in Paris. "Politics is not the nicest business in the world, but it's very standard where they have information and you take the information."

Earlier this week, Donald Trump Jr. revealed email correspondence showing he was told the potentially incriminating information about Clinton would be coming from the Russian government, before he arranged the June 2016 meeting with Kremlin-linked lawyer Natalia Veselnitskaya in Trump Tower.

As some lawmakers and legal experts questioned whether his namesake broke campaign finance laws or improperly colluded with Russia, President Trump stressed that his son's meeting was not a formal Russian government official. He also insisted that it was a "short meeting" and the lawyer did not provide any information on Clinton.

"Zero happened from the meeting," Trump said.

Insisting that "from a practical standpoint most people would've taken that meeting," President Trump also called his son "a wonderful young man" and "a fine person."

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Like his father, the younger Trump said this week that he thought the meeting was part of standard opposition research, and that he did not realize the potential ramifications of meeting with a foreign national on the subject. The meeting was also attended by former campaign chairman Paul Manafort and Trump son-in-law Jared Kushner.

Trump Jr. said the lawyer did not have information on Clinton, but only wanted to talk about U.S. sanctions on Russia.

Still, some lawmakers have said that, even if Trump Jr. did not receive damaging information on Clinton, his apparent eagerness to take the meeting after being told the source of the information was from Russia could spell trouble.

Multiple congressional committees and a special counsel are investigating whether there was any collusion between Trump associates and Russians who tried to influence the election in favor of Trump by hacking Democrats close to Clinton and leaking stolen information to websites such as WikiLeaks.

Sen. Chuck Grassley, R-Iowa, chairman of the Senate Judiciary Committee, said Thursday he would send Trump Jr. a letter asking him to testify about the incident as soon as possible.

What's more, campaign and ethics experts have also disputed the Trumps' claims that the meeting constituted normal opposition research.

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“I don’t know many people who would have done this,” Larry Noble, a former top Federal Election Commission lawyer who is now at the nonpartisan Campaign Legal Center, told USA TODAY on Wednesday. “Most people have this sense that American elections should not be influenced by foreign interests.”

“It's called spying, not opposition research,” Richard Painter, President George W. Bush’s former ethics lawyer and a frequent critic of President Trump’s activities, said about any information gleaned from Russian sources during the 2016 campaign.

The younger Trump has also faced legal questions about whether his meeting violated federal campaign laws. It’s illegal to solicit or accept a contribution from a foreign entity, and opposition research could be considered an in-kind contribution.

Three watchdog groups – Common Cause, Democracy 21 and the Campaign Legal Center – on Thursday filed new complaints with the Department of Justice and the Federal Election Commission, contending that Donald Trump Jr. breached federal law along with the meeting’s other attendees, Manafort and Kushner.

“The e-mails released by Donald Trump Jr. reveal, in no uncertain term, his choice to place his blind support for his father’s candidacy before any allegiance to the nation’s security,” Common Cause President Karen Hobert Flynn said in a statement.

“Democracy is not a real estate deal or a New York solid waste pickup contract,” she said, “but that is how these three Trump campaign officials treated it in agreeing to meet to accept opposition research they believed came from the Russian government.”

The president has said he did not know about the 2016 meeting until just recently; Donald Trump, Jr., also said he did not tell his father about the meeting because it didn't produce anything.

"There was nothing to tell," Trump Jr. told Sean Hannity of Fox News.

Trump and Macron spoke to reporters after a series of meetings in Paris in which the leaders pledged cooperation on issues like counterterrorism and maintaining a ceasefire in Syria, even as they continued to disagree on what to do about climate change.

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Macron said he still disputes Trump's decision to withdraw the United States from the Paris climate change agreement, and hopes to work with the U.S. on joint ways to address the problem. "It is important that we can continue to talk about it," he told Trump.

Trump, who argued that the Paris deal was unfair to the United States, suggested he is willing to look at it again, but did not make any promises. "Something could happen with respect to the Paris Accord," he said. "We'll see what happens."

The two presidents said they disagree on issues – and Trump is unpopular in France generally – but they have a positive working relationship.

"I'm coming back," Trump told Macron. "You better do a good job, please, otherwise you're going to make me look very bad."

The French president, who like Donald Trump Jr., is 39 years old, replied: "You're always welcome."