The admission is a complete reversal from prior explanations of the meeting.
Donald Trump has labelled reports that he is concerned over the legality of his son's Trump Tower meeting with a Russian lawyer as "fake news", and said getting dirt on 2016 presidential rival Hillary Clinton was "totally legal". He also said the meeting was "totally legal" and he did not know about it. Weija Jiang reports.
In one tweet, he declared the media the "Enemy of the People" and accused outlets of sowing division and distrust.
Former White House communications director Anthony Scaramucci says President Trump's attacks on the media are "very bad for the country".
Trump was apparently responding to reporting from The Washington Post and other outlets that the president has been increasingly brooding in private about the Mueller probe, particularly as it relates to his son's possible entanglement in the investigation.
The misdirection came amid a series of searing tweets sent from Trump's New Jersey golf club. At the time, Trump and his White House had falsely claimed that he had only offered his input into the crafting of the statement.
But since then, the story about the meeting has changed several times, eventually forced by the discovery of emails between the president's eldest son and an intermediary from the Russian government offering damaging information about Trump's opponent, Hillary Clinton. When asked about the shirts, Alicie said he didn't understand why Trump faces so much criticism about Russian Federation, while Hillary Clinton and Barack Obama didn't, and Alicie encouraged Democrats, "To jump on board this train and give him a chance".More news: YEMEN: Air strikes on fishing port in Hodeidah kill 26
A senior Republican lawmaker on Sunday urged Trump to acknowledge to Americans that Russia's interference in US elections is still a threat, something Moscow denies.
While Trump and his surrogates have made similar claims before, many observers noted that the tweet appears to be evidence of criminal activity - that is, soliciting valuable campaign assistance from a foreign power.
The president admitted that the objective of the meeting was to get information about his Democratic rival.
"So when you look at a meeting - when you look at a meeting, George, that took place in - a - a year before the (ph) - now two years ago, the question is what law, statute or rule or regulation's been violated?"
Sunday's tweet was Trump's clearest statement yet on the objective of the meeting, which has become a focal point of Mueller's investigation even as the president and his lawyers try to downplay its significance and pummel the Mueller probe with attacks.
Others have said the meeting could provide clues to a broader conspiracy by Trump officials with Russians.