In 2007, Sliwa announced an intention to reinvigorate New York City's Republican party, and possibly run for office. In 2013, Sliwa endorsed Republican candidate
John Catsimatidis for mayor. In September 2016, Sliwa and
Frank Morano launched a successful
hostile takeover of the
Reform Party of New York State. The Party lost its ballot access in
the November 2018 elections.
2021 mayoral campaign Sliwa announced on March 8, 2020, that he would run for mayor of New York City in 2021 as a
Republican. The primary race turned Sliwa and
Fernando Mateo, once friends, into bitter rivals. The Manhattan, Queens, and Bronx Republican parties endorsed Mateo, while the Staten Island and Brooklyn Republican parties endorsed Sliwa. During the campaign, Mateo and Sliwa clashed over loyalty to former president
Donald Trump. Mateo voiced support for Trump's claim that
he won the 2020 presidential election; and does not support Trump's
election denial. Sliwa ran on a platform opposing the
defund the police movement, supporting a property tax overhaul so that working-class residents would not pay higher property taxes than wealthy citizens, keeping in place the
Specialized High Schools Admissions Test while increasing opportunities for vocational training in charter schools, and focusing on fiscal restraint. He also opposed the killing of unwanted animals and supported making all animal shelters
no-kill shelters, pointing to his own home life with 16 cats. Sliwa campaigned on beginning a trial program to test out the feasibility of
universal basic income in New York City. Sliwa lost to Brooklyn Borough President
Eric Adams in a landslide defeat in the general election on November 2, 2021, with Adams winning just over two-thirds of the votes. Sliwa conceded that same night, calling for unity in order to save New York City. After his loss, he brought two cats outside the Brooklyn home of Adams in January 2023, after the latter had been fined for rodent violations, and suggested that feral cats could address the rodent problem in the city.
2025 mayoral campaign On February 13, 2025, Sliwa announced his candidacy to run for mayor of New York City in 2025, again as a Republican. During his candidacy, he apologized for past statements regarding the city's
Hasidic population and criticized
ICE's detainments of immigrants coming to courthouses for appointments and deportation without
due process: "everybody gets due process in the United States." A mid-July 2025 poll of registered NYC voters found Sliwa coming in third, with 13%. The pattern continued into early September, with Sliwa placing third, after Democratic nominee
Zohran Mamdani and
independent candidate Andrew Cuomo, but ahead of incumbent mayor
Eric Adams. Throughout the election, Sliwa rejected calls for him to exit the race in order to help defeat Mamdani, including pressure from Trump and, Sliwa said, from billionaires who had offered to pay him to drop out. In spite of strong opposition from various billionaires and national Republicans to stay in the race, Sliwa received support from most GOP leaders in the five boroughs. In response to Andrew Cuomo calling Sliwa a "
spoiler" and saying that "Curtis will make Mamdani a winner", Sliwa stated, "I suggest Andrew Cuomo come off his high horse. If he wants to win this election, go out and campaign for your voters." It was debated whether or not Sliwa ending his campaign would have helped in boosting Cuomo's campaign and defeating Zohran Mamdani. An
AARP poll conducted in October showed Cuomo with 41% against Mamdani's 44% if Sliwa were to step aside, within the poll's margin of error. A spokesperson for the Sliwa campaign has said, "The overwhelming majority of Sliwa supporters would not touch Andrew Cuomo with a ten-foot pole." Sliwa received 7% of the vote, placing behind both Cuomo, and Mamdani who won the election with over 51% of the vote. ==Political positions==