The GOP debate field is set - here's who's in and who's out

The field is set for the fourth Republican debate, and there have been several major shakeups.

On Thursday, Fox Business announced the lineup for the debate, which will be hosted next Tuesday in Wisconsin.

Two GOP heavyweights - New Jersey Gov. Chris Christie (R) and former Arkansas Gov. Mike Huckabee (R) - fell short of the 2.5% polling average in the four latest national polls needed to qualify, and will not participate in the main stage debate.

The remaining candidates from the previous debate - real-estate mogul Donald Trump, retired neurosurgeon Ben Carson, Sen. Marco Rubio (R-Florida), Sen. Ted Cruz (R-Texas), former Florida Gov. Jeb Bush (R), Ohio Gov. John Kasich (R), Sen. Rand Paul (R-Kentucky), and former Hewlett-Packard CEO Carly Fiorina - all qualified.

In addition, Sen. Lindsey Graham (R-South Carolina) and former New York Gov. George Pataki (R) failed to garner the 1% support in at least one of the latest four national polls needed to participate in the so-called "undercard" debate, which will be broadcast earlier on Tuesday evening on Fox Business.

Christie, Huckabee, Louisiana Gov. Bobby Jindal (R), and former Sen. Rick Santorum (R-Pennsylvania) qualified for the lower-tier debate.

Christie has started to see his polling numbers rise slightly in New Hampshire, a key early-voting state, but that hasn't yet translated into national momentum. Huckabee's numbers have also fallen steadily since he entered the race earlier this year.