The chairman said the objective of these investigations is to inform "the American people about obstruction of justice, corruption, and abuse of power".
"I am an innocent man being persecuted by some very bad, conflicted & corrupt people in a Witch Hunt that is illegal & should never have been allowed to start", Trump said in a tweet on Sunday.
House Judiciary Committee Chairman Jerry Nadler (D-NY) on Sunday said it's "very clear" that Donald Trump committed obstruction of justice, making the case in an interview with ABC's George Stephanopoulos. Before you impeach somebody, you have to persuade the American public that it ought to happen.
Trump set off a political firestorm by firing Federal Bureau of Investigation chief James Comey on May 2017 - and then admitting to NBC he had taken the decision after becoming frustrated with the Russian Federation probe. "We will do everything we can to get that evidence".
On "This Week", Nadler also cited what he called Trump's attempts to intimidate witnesses in the investigation.
Eurotunnel withdraws suit after $43 million Brexit deal
As time marches on and this becomes clearer to our MPs, the risk is that they do, in the end, cave in to Mrs May's bad deal.
"They're discrediting America and they dislike this president so much they won't give him an opportunity to try to denuclearize North Korea that they would have a hearing on that day", he said. "But we're going to initiate proper investigations", Judiciary Committee Chairman Jerrold Nadler said.
Nadler's announcement came just days after another House committee publicly questioned the president's former personal lawyer, Michael Cohen, who implicated Trump in several serious crimes, including potential campaign finance violations connected to hush-money payoffs to women and possible fraud charges concerning falsified documents provided to banks and insurance companies.
That investigation was subsequently taken over by Special Counsel Robert Mueller, who is expected to deliver his findings to the United States attorney general within weeks. But he said he was personally convinced that Trump has obstructed justice - an offence that was included in the impeachment articles passed in the House against both Richard Nixon and Bill Clinton.
Besides Comey's firing, prosecutors appear to be examining Trump's role in crafting the misleading Air Force One statement in 2017 on the now-infamous June 2016 Trump Tower meeting with Russians attended by Trump Jr. We don't have the facts yet.
Republican Adam Schiff, who chairs the House intelligence committee, also stressed that it's too early to make judgments about impeachment. "I still don't know, they don't have to tell me, but I still don't know whether anyone in the Trump administration at the most senior levels ever got a read out".