The younger Trump is a key player in the controversy over Russia's meddling in the 2016 election. According to emails released by Trump Jr.,
he met on June 9, 2016 with Natalia Veselnitskaya, a lawyer
who was described to him as an emissary of the Russian government with information that was part of the country's effort to help elect his father.
"My son Donald did a good job last night," President Trump wrote on Twitter. "He was open, transparent and innocent. This is the greatest Witch Hunt in political history. Sad!"
Trump Jr. chose a friendly venue, Fox News, to downplay the meeting Tuesday night, saying, "I probably would have done things a little differently."
Shortly after the President's first tweet Wednesday, he added, "Remember, when you hear the words 'sources say' from the Fake Media, often times those sources are made up and do not exist."
Trump Jr., though, released the emails on his own on Tuesday, tweeting them out after The New York Times contacted him with questions about the emails they had obtained.
The President later lashed out against his 2016 Democratic opponent, charging her with unspecified wrongdoings.
"Why aren't the same standards placed on the Democrats. Look what Hillary Clinton may have gotten away with. Disgraceful!" he tweeted
Despite Trump Jr.'s dismissals, the issue grew more serious for him when a US official briefed on the matter told CNN that special counsel Robert Mueller's investigators plan to examine the meeting and email exchanges
disclosed by Trump Jr. as part of the broader Russian-meddling investigation.
The details of the interactions weren't fully known to investigators until recently, according to three US officials familiar with the probe.
President Trump's tweet is a familiar take on the Russia controversy. The President, who has long denied any collusion between his campaign and Russian operatives, has argued for months that the inquiry is a "witch hunt"
of epic proportions.
"You are witnessing the single greatest WITCH HUNT in American political history - led by some very bad and conflicted people," Trump tweeted in June.
In May, he wrote that the probes -- including multiple investigations on Capitol Hill -- were "the single greatest witch hunt of a politician in American history!"
Until Tuesday, Trump had been silent on Twitter when it came to his son, instead choosing to tweet about the recent G20 summit in Germany
and a defense of his daughter, Ivanka Trump,
who stirred controversy when she briefly sat in Trump's chair during a meeting with world leaders.
Trump, through a spokeswoman, defended Trump Jr. on Tuesday in a brief statement.
"My son is a high-quality person and I applaud his transparency," he said in a statement.
This story is being updated.