Progressive Aisha Wahab was elected to Congress in a special election on Tuesday following a bitter intra-party battle over the seat formerly held by Eric Swalwell, who resigned in April after facing sexual misconduct allegations. Swalwell has denied the allegations.

Wahab, a state senator, was widely considered the frontrunner in the district in California’s East Bay and had the backing of the state Democratic party as well as Our Revolution, labor unions, local officials and the state’s attorney general, Rob Bonta. She won the primary for the special election for the final months of Swalwell’s term by more than 20 points over Hernandez, the president of the board of directors for the Bay Area Rapid Transit (Bart) agency.

While Wahab held a major lead throughout the race, Hernandez’s campaign received a significant boost as Super Pacs connected to the American Israel Public Affairs Committee (Aipac) poured money into the race. With 92% of votes counted on Thursday afternoon, Wahab led Hernandez by just over six points – a much closer race than expected.

Earlier this month, it emerged that Super Pacs had spent more than $5m in a matter of weeks on pro-Hernandez ads and Wahab attack ads. Track Aipac, which monitors the group’s funding of US politicians, recently reported that the lobby had spent nearly $6.4m to support Hernandez.

Wahab, the first Muslim woman and Afghan American elected to the California legislature, told the Guardian there had been a sudden surge of critical ads that had misrepresented her record. She described the Super Pacs’ involvement as election interference, and said they were attempting to buy the seat.

The race further intensified in recent days after the congresswoman Zoe Lofgren, chair of California’s Democratic delegation, endorsed Hernandez. Lofgren said Wahab did not back an effort to elect a caretaker candidate in order to fill Swalwell’s seat as quickly as possible.

But the progressive wing of the party strongly supported Wahab, with a former chair of the progressive caucus of the California Democratic party, Amar Shergill, telling Politico that Lofgren’s actions were “astounding”, and continued backing Wahab amid the upheaval in the race in recent weeks.