Here’s What You Missed at The First Two Republican Presidential Debates

— -- The Republican presidential candidates will meet Wednesday night for their third debate.

This time, CNBC's Carly Quintanilla, Becky Quick and John Harwood will be grilling the GOP candidates on jobs, taxes, the deficit and the health of the economy among other issues at the University of Colorado in Boulder. Before the 10 top polling candidates grace the stage at 8 p.m. ET, the so-called "undercard candidates" will try to make their case in a 6 p.m. ET faceoff.

But there have been some big changes since the first time the candidates all met on stage: Gov. Scott Walker and former Gov. Rick Perry are no longer in the race, Ben Carson is emerging as a major threat to Donald Trump’s frontrunner status, and Carly Fiorina has broken into the boy's club.

In case you missed them or just need a refresher, here’s a quick wrap of the first two Republican debates:

First GOP Debate, Aug. 6, Cleveland, Ohio

At the Fox News-hosted debate, the spotlight was squarely on Donald Trump. Right off the bat, the New York businessman got boos from the audience for refusing to pledge support to the Republican nominee for president -- unless it's him.

"I will not make the pledge at this time," Trump said.

Ben Carson, who is now Donald Trump's toughest competition in the race, barely got any speaking time in this debate. He even admitted, "I wasn't sure I was going to get to talk again."

New Jersey Gov. Chris Christie and Sen. Rand Paul butted heads over national security and Americans' privacy, while Jeb Bush sometimes looked uncomfortable on stage.

At the time, former Hewlett Packard CEO Carly Fiorina wasn’t polling high enough to participate in the main debate, but her performance in that undercard debate was enough to catapult her onto the main stage for the second Republican debate.

Second GOP Debate, Sept. 16, Simi Valley, California

CNN's debate at the Ronald Reagan Presidential Library in Simi Valley, California, had the same 10 candidates as the first debate plus one.

Enter Fiorina. She had a big night, responding to Trump's "face" comments he made in a Rolling Stone interview and the two argued over business records. She also got loud applause for her comments on Planned Parenthood.

Other memorable moments included Bush’s admission that he smoked pot, the awkward handshake (or was it a high-five?) between Carson and Trump, and Bush's demand that Trump apologize to his wife.