Victories by the progressive left in last week’s Democratic Party primaries have left the real estate industry reeling, with fears that landlords and developers could lose out if Democrats take complete control of the state government in November.

Republicans, who now maintain a narrow majority in the Senate — and until recently with support from a rogue group of Democrats aligned with the GOP — have been a “firewall” blocking pro-tenant legislation that would eliminate or scrap the ability of landlords to boost rents, a knowledgeable source in the real estate industry said.

“The Republicans have a problem. The momentum is against the Republicans,” the industry insider said.

The sea change in Albany could come even after landlords and developers pumped millions of dollars into the campaign coffers of pro-business Republicans and friendly Democrats over the years.

The political tsunami last week wiped away real estate pals, such as Bronx Sen. Jeff Klein, the former Senate leader who headed the disbanded Independent Democratic Conference that often voted with the GOP.

The challenger who defeated Klein, Alessandra Biaggi — granddaughter of the late Rep. Mario Biaggi — told The Post that tightening tenant protections will be among her top priorities.

And Julia Salazar, a Democratic socialist who will likely represent the gentrified Brooklyn neighborhoods of Williamsburg, Greenpoint and Bushwick — ground zero in the rent wars — defeated eight-term incumbent Martin Dilan.

Salazar — who was elected despite falsely claiming that she graduated from Columbia University — effectively portrayed Dilan as a tool of real estate interests for taking money from them, and will champion pro-tenant measures.

“The real estate people are nervous,” said one Albany source. “They’re trying to find new friends in the Senate Democratic Caucus.”

The pro-tenant lobby said the political wind is at their backs to seriously address the housing affordability crisis for working-class renters.

“I am pumped!” said tenant activist Mike McKee, who stumped for Biaggi. “We have a real chance not just to close loopholes in the rent laws but to reshape the whole system.”

No matter the outcome in November, McKee and real estate insiders agree that a first test will take place early in 2019, when Gov. Andrew Cuomo and lawmakers have to act to renew the rent regulation law covering 1 million rent-stabilized and rent-controlled apartments in New York City. The law expires in mid-June.

Approval of such anti-business measures will dry up investment in the city’s affordable housing market, which includes rent-stabilized apartments, the knowledgeable real estate industry source warned. Curbing the ability to recover money for capital repairs will make banks leery to lend to landlords, the source added.

The insider said to be careful what you wish for.

“These young people don’t remember what the Bronx looked like in the 1960s and 1970s, when there was disinvestment and boarded-up and vacant buildings,” the source said.