Spencer Pratt is Karen Bass’ biggest threat in the race for Los Angeles mayor … at least according to the Bass campaign’s own internal pollster.

An email sent Thursday by Bass campaign advisor Douglas Herman to “Interested Parties” — including endorsers and supporters — states that the campaign’s internal pollster, Binder Research, currently shows Pratt in position to make the November runoff.

The letter — obtained by TMZ — also takes direct aim at Nithya Raman, the L.A. City Councilmember and progressive who entered the race late and is widely viewed as a key challenger.

Herman argues Raman is nowhere near the level of NYC Mayor Zohran Mamdani in terms of “name awareness, unified base or favorable appeal” … adding that with just over 70 days until primary ballots are mailed to voters, she faces a steep uphill climb.

Earlier this month, we caught up with Spencer at a campaign event, where he confidently predicted an easy victory — and even suggested Bass could end up in jail, referencing an L.A. Times story alleging she directed changes to a report detailing the LAFD’s response to the Palisades Fires. Bass has flatly denied the claims.

On the flip side … Spencer is apparently having having trouble getting all his family members on board with his mayoral bid — his sister, Stephanie, blasted his candidacy, saying “A vote for him is a vote for stupidity.”