The repercussions for candidates in the first two sets of Democratic presidential primary debates have tended to be short-lived, according to Brit Hume.

In the few weeks after the first debate's fireworks between Sen. Kamala Harris, D-Calif., and former Vice President Joe Biden, the long-term impact appears muted for both contenders, Hume claimed Wednesday on "Special Report."

"It is awfully early still and I think what we have to be alert to is the likelihood that whatever effects these debates seem to be having on the race [are] not very permanent," he said.

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Pointing to the exchange between Harris and Biden in June, where the California lawmaker criticized the Delaware Democrat for his work with segregationist former senators regarding busing, Hume said both appear to be in the same straits they were before the forum.

"He's back up to about where he was, and she has sunk again," he said.

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"Which suggests, people at this stage are not reacting very strongly and their impressions are impermanent and soft. Whatever comes out of these two nights -- I question whether the effects will last very long."

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Later Wednesday, Biden and Harris are set to face off again on the debate stage, along with Sen. Michael Bennet, D-Colo., New York City Mayor Bill de Blasio, Sen. Cory Booker, D-N.J., Washington Gov. Jay Inslee, Andrew Yang, former HUD Secretary Julian Castro, Sen. Kirsten Gillibrand, D-N.Y., and Rep. Tulsi Gabbard, D-Hawaii.

With the Democratic National Committee raising the thresholds for the third and fourth rounds of debates -- in September and October -- the showdowns this week may be the last chance for many of the lower-tier candidates to make a splash in front of a prime-time national audience.

Fox News' Paul Steinhauser contributed to this report.