Given just how much has changed in the GOP race after the first debate and given the upcoming end to the fundraising quarter (Sept. 30), the pressure is on for the 11 Republican candidates to perform at tonight's second debate in California at 8:00 pm ET.
We'll find out which of the second-tier candidates -- think Walker, Paul, Rubio, Christie, Huckabee, and Kasich-- moves up or falls back.
Meanwhile, Trump needs to keep defying political gravity and put some policy meat on the bones while Ben Carson must keep the momentum he has in the polls. Jeb Bush should be prepared for other candidates to come after him.
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Click through for more analysis on what each candidate needs to do at tonight's debate.