During her time to ask questions, Rep. Alexandria Ocasio-Cortez, D-N.Y., said the allegations are "extremely serious," but called the hearing an "embarrassment."

She established that none of the four witnesses can give any firsthand witness account of any crimes committed by the president.

"This is an embarrassment. It is an embarrassment to the time and people of this country," she said.

Rep. Glenn Grothman, R-Wis., followed by saying he was concerned about the "seriousness of the allegations."

"We have all sorts of smoke, maybe not fire," he said. "It deserves a strong response from this body."

Rep. Shontel Brown, D-Ohio, asked Democratic witness Michael Gerhardt what he believes is the "primary flaw" in the Republican claims about President Biden.

"Well, I suppose I can say a lot. The problem is the dots are not connected," Gerhardt replied. "The name repeated most often is Hunter Biden, not President Biden. And the point of an impeachment inquiry is not about a president's son, it has to be about the president himself and I don't think those dots connected. Lots of assumptions and accusations, not evidence."

Rep. Jim Jordan, R-Ohio, chairman of the House Judiciary Committee, called testimony from Hunter Biden's former business partner, Devin Archer, "the most telling evidence" of the president's potential involvement in an "influence-peddling scheme."

Jordan said that a Ukrainian prosecutor investigating a Ukrainian company tied to Hunter Biden's was fired after Hunter Biden received a request from Burisma's top executive and then called his father, who "leveraged $1 billion of American tax money" to get the prosecutor fired.

But a review of Archer's testimony, detailed in a publicly-released transcript, shows that Jordan left out key parts of Archer's testimony and mischaracterized other parts of it.

Among other things, Archer said the request from Burisma's top executive wasn't specific to the prosecutor's firing, and he wasn't even sure that Hunter Biden called his father after getting the request.

--ABC News' Mike Levine and Luc Bruggeman

Democrats again tried to force a vote on subpoenaing Trump ally Rudy Giuliani over his alleged efforts to dig up dirt on the Biden family's business dealings in Ukraine and Biden's actions as vice president. Republicans were able to successfully kill the motion.

Chairman Comer attempted to dispense of the motion with voice vote but Democratic Rep. Jamie Raskin pushed for a recorded vote. It failed 20-18.

"Where in the world in Rudy Giuliani?" Rep. Kwesi Mfume, D-Md., bellowed, holding up a piece of paper that read the same.

The committee is expected to reexamine the findings of months of GOP-led investigations and offer an explanation as to why an inquiry is warranted.

"This week, the House Oversight Committee will present evidence uncovered to date and hear from legal and financial experts about crimes the Bidens may have committed as they brought in millions at the expense of U.S. interests," chairman James Comer, R-Ky., said in a statement.

The committee will hear from four witnesses, three of whom were called by Republicans to provide testimony.

The panel's 46 members (plus other lawmakers) will be allowed to question the witnesses in a hearing that could stretch on for more than six hours.

Read more about what to expect from the hearing here.