"I think it's really important for us not to normalize the behavior of this president and this administration," freshman Congresswoman Ilhan Omar said.
"The way he's acted as president has been completely at a detriment to our nation's unity," a veteran said of Trump.
"The frustration is that there's no bar, there's no line in the sand that we're waiting for in order to trigger impeachment," the freshman Democrat said.
Robert Mueller's testimony will offer Democrats the first chance since the release of his report to directly question the former special counsel.
Trump's relentless obstruction means that an impeachment inquiry is now the only viable option to reveal the facts and to hold him accountable.
Impeachment continues to be a thorny topic for Democrats. For the most part, leaders of the party have argued that impeachment is a politically risky move.
There are now three House Democrats considered vulnerable in 2020 by the fundraising wing of the party who support an impeachment inquiry, potentially putting themselves—and Democrats' House majority—at risk by supporting impeachment in divided districts.
"I think it would be good for them to make a little more progress," former acting FBI Director Andrew McCabe said.
The NRCC wrote that Porter "is so consumed by her hatred of President Trump" that she has decided to come out in favor of impeachment.
The "Last Week Tonight" host took aim at the U.S. president.
"Opening an impeachment inquiry is exactly what we must do when the President obstructs justice, advises witnesses to ignore legal subpoenas, & more. Bye,"," the New York congresswoman said on Twitter.
Ocasio-Cortez said Trump's comments that he was open to accepting foreign help for "dirt" on 2020 rivals shows members of Congress have a "duty" to at least consider impeachment.
Sunday's Fox & Friends mocked low attendance at several Trump impeachment rallies over the weekend, with the president himself giving the hosts several shout-outs on Father's Day.
"It is our duty as members of Congress to pursue the last option we have in this pursuit of justice on behalf of the American people," Tlaib said.
"See you soon Justin..." Trump Jr. tweeted. "I hear Michigan is beautiful during primary season."
"I think the idea that [impeachment] is a clear political loser for Democrats is just something that is not supported by the evidence of 1998 and 2000," CNN senior political analyst Ron Brownstein said.
"It's time for every lawmaker in Congress to go on the record about whether they believe Trump's criminal conduct is acceptable," said Sean Eldridge, Stand Up America's founder and president.
Nature doesn't do subpoenas: it does tornadoes, floods, wildfires and droughts. No leader can stonewall it.
The public hearings will play a crucial role in Democrats' ability to highlight what they believe was wrongdoing by Trump. Some Democrats will likely use the opportunity to make their case why the House should open an impeachment inquiry, a move that a growing number of party members have called for since the Mueller report's release.
The figures vary wildly by political affiliation, but overall there has been an uptick in support for the process.
"Mueller, I'd imagine, at the behest of the left gives them what they need to jumpstart the calls for impeachment," Jeanine Pirro said. "You either indict or you don't… every prosecutor knows if you don't indict someone, you stop there."
"We have a constitutional republic to uphold liberty and the Rule of Law, not a direct democracy to serve some at the expense of others," Rep. Justin Amash (R-Mich.) said.
Republicans "know there is a damning case in the Mueller report of obstruction of justice by the president and they are acting like there's not. And that's just flatly dishonest," Donald Ayer, deputy attorney general under former President George H. W. Bush, said.
"We will build an ironclad case to act," Pelosi said, holding off calls for impeachment.
"Take the word impeachment away. It's a losing word," he said. "It's a 30-year-old word that does not help us."
Not only did those who already support impeachment proceedings view Mueller's statement as a call to action, more Democrats piled on, saying it was now time to initiate the significant measure of an impeachment inquiry.
"It's a can of worms, it's a new headache that the president doesn't need, it advances the law into Congress' court," Andrew Napolitano said.
Republican CNN guest Rick Wilson misquoted a line from HBO's "The Wire," in which he warned Nancy Pelosi to go all-in on impeachment if she chooses to, because "if you're going to go after the king, you best get him."
"These facts that he laid out are so substantially similar to the matured allegations against Bill Clinton and Richard Nixon, it's clear where he was going," Andrew Napolitano explained.