Brooklyn Councilman Ari Kagan officially switches parties and will run as Republican in Bay Ridge district

Brooklyn City Councilman Ari Kagan officially became a Republican on Monday, saying he will switch districts to run against a fellow incumbent next year.

Kagan, who was elected just last year to represent a Coney Island-based district, said he has joined the Republican caucus in the Council and will challenge Councilman Justin Brannan in a rejiggered district in nearby Bay Ridge.

“Every month I was asking myself, ‘Why am I still a Democrat?’” Kagan said in a press conference on the steps of City Hall. “It’s not about numbers or an election. It’s about [sending] a message.”

[ EXCLUSIVE: Coney Island councilman plans switch to GOP ]

The Daily News first reported Kagan’s plans on Sunday night.

Kagan, an immigrant from Belarus, was flanked by Republican Minority Leader Councilman Joe Borelli (R-Staten Island).

Kagan stressed rising crime as the No. 1 issue behind his decision. He also said Democrats were unresponsive to demands to moderate the party’s liberal stances.

“I didn’t leave the Democratic Party. The Democratic Party left me,” Kagan said.

He said he will run in a neighboring 43rd Council district because he feels betrayed by fellow Democrats in his own 47th district, which was dramatically redrawn by an independent redistricting commission.

Unsurprisingly, Kagan’s move drew Bronx cheers from Democrats, who branded him a turncoat.

“This is just pure political opportunism,” Brannan said.

“This drastic about-face seriously calls into question [Kagan’s] commitment to [Democratic] policy priorities,” Council Speaker Adrienne Adams (D-Queens) said in a statement.

Mayor Adams was more circumspect, saying ahead of the press conference that Kagan “has to [do] what he thinks is best.”

Kagan’s move comes as Republicans have been enjoying a major revival in south Brooklyn.

Three GOP candidates flipped Democratic districts in the area in the midterms, although Democrats are threatening not to seat Assemblyman-elect Lester Chang, claiming he really lives in Manhattan.

Rep. Nicole Malliotakis (R-N.Y.) also had a much bigger-than-expected victory over former Democratic Rep. Max Rose in the NY-11 congressional district that includes the neighborhoods represented by Brannan and Kagan.