The angry accusation came as Attorney General Jeff Sessions -- a close Trump confidant and the US government's top law enforcement official -- was forced to recuse himself from any Russia-related inquiries.
After Sessions told senators under oath that "I didn't have -- did not have communications with the Russians," journalists uncovered he had actually met the Russian ambassador twice in the months before taking office.
The meetings have raised red flags for Democrats, who have called for Sessions to resign and be investigated for perjury.
Trump said he had "total" confidence in Sessions, who "could have stated his response more accurately" but "did not say anything wrong."
Trump also lashed out at leading Senate Democrat Chuck Schumer.
Trump tweeted an old picture of the senator with Russian President Vladimir Putin along with the caption: "We should start an immediate investigation into @SenSchumer and his ties to Russia and Putin. A total hypocrite!"
Since US intelligence took the unprecedented step of publicly accusing Russia of trying to swing the November election in Trump's favor, questions have swirled about whether some in Trump's campaign colluded with Moscow.
Trump has repeatedly denied any personal ties to the Kremlin, and his aides have variously denied or played down contacts with Russian officials.
But it has now emerged that a slew of associates aside from Sessions and already fired national security advisor Michael Flynn met Moscow's envoy to Washington, Sergey Kislyak, before Trump took office.
US media reported that advisors JD Gordon and Carter Page met Kislyak and, separately, that Flynn and Trump's son-in-law and senior White House aide Jared Kushner met Kislyak at Trump Tower in New York last December.
Sessions' own meetings with the envoy took place much earlier, in July and September, just as accusations of Russian interference in the election were mounting, according to The Washington Post.
According to officials, US intelligence agencies and the Federal Bureau of Investigation continue to investigate just how and how much Moscow intruded into US politics.
Four congressional committees have opened probes into the issue, although Democrats fear Republicans will seek to bury their investigations to protect Trump's young administration.
Trump's White House has lobbied the FBI, reportedly the CIA and two Republicans who head committees leading investigations into Russia's election meddling to knock down media reports on the alleged links.
The latest furor has come at a terrible time for Trump's White House.
Earlier this week, Trump delivered his maiden address to Congress, a speech that was well received and offered an opportunity to turn the page on 40 tumultuous days in office.
His address was widely praised -- he adopted a more measured tone, which rounded the sharper edges of his nationalist rhetoric.
Trump could have expected a bounce in the polls.
His approval rating currently stands at 43 percent, according to Gallup -- a historic low for a modern president this early in his term.
Apart from dealing with allegations about Russia ties, much of the last month has been spent dealing with a contentious travel ban on citizens from seven majority Muslim countries.
jpegMpeg4-1280x720Trump's first order was knocked down by the courts and a second order has been repeatedly delayed.
The latest expected deadline -- Wednesday -- came and went.
"When the president has made a decision about something that he's ready for us to announce, we'll announce it, but we're not there yet," spokesman Sean Spicer said Thursday.