(CNN) When Sen. Kamala Harris of California went on the offensive against former Vice President Joe Biden in the June debates, one could envision that the primary race had been forever changed. Biden looked like he had no answers for the aggressive former prosecutor.

A look at recent polls indicate, however, that while Harris' chance of winning is higher than it was before the first debate, she'll likely need another strong performance tonight to be considered a front-runner.

The first three live interview national polls following the June debates had Harris shooting up. She jumped from 7% in an average of polls before the debate to 17% in the polls taken in the week following the debate. That was one of the largest debate bounces that I found in recent presidential primary history

But the three live interview polls ( Fox News NBC News/Wall Street Journal and Quinnipiac University ) taken in the period after the immediate aftermath suggest that Harris has come back to earth. She's averaged only 12%. That puts her in fourth place behind Biden (31%), Massachusetts Sen. Elizabeth Warren (15%) and Vermont Sen. Bernie Sanders (13%).

It shouldn't be too surprising that Harris fell back. Debate bumps often are only momentary. Even the largest bounces recede.

Perhaps what is more important for Harris' future is that she is in a better polling position than she was prior to the first set of debates, and it may have some staying power. Instead of being tied with South Bend, Indiana, Pete Buttigieg at 7%, she's now 6 points ahead of his 6%.

The first debate also seems to have convinced members of Congress to come off the sidelines for her. Before the first debate, Harris had only three endorsements from congressmen outside her home state. Since the first debate, she's gotten four more endorsements, more than doubling her endorsement count from members of Congress outside California (though she still trails in the endorsement race -- Biden has 13 endorsements from congressmen outside of his home state of Delaware).

Endorsements, of course, have been correlated with primary success in prior years.

So will the second debate provide the boost Harris needs? It probably depends as much on Biden, who will be standing beside her onstage, as it does Harris. He claims he was unprepared for the attacks from Harris in Miami. Biden won't be this time around.

Perhaps most worrisome for Harris is that her support among African Americans doesn't seem to have risen much as you might have thought after going after Biden on his 1970s opposition to desegregation busing. Harris initially seemed to have a breakthrough and was averaging 21% with black voters in the three polls taken just after the June debates. Since then, Harris is averaging 12% among black voters in national polls. Again, that's up from where she was before the first set of debates -- but It's still well behind Biden's 50% in these same polls.

If Harris hopes to build on her first debate success, she'll likely need to find a way to retake some of Biden's black voter base.