In a slap at President Obama, former President Bill Clinton will headline a fundraiser for a New York congresswoman challenging White House-backed Sen. Kristen Gillibrand in the state's Democratic primary.

Clinton has not endorsed in the race, but his efforts to help Rep. Carolyn Maloney could be seen as a snub to Gillibrand and the Obama White House. Matt McKenna, a spokesman for Clinton, said he will be attending a July 20 fundraiser in New York.

The White House has played an active role in clearing the field for Gillibrand, who was appointed earlier this year to fill the seat vacated when Obama tapped Hillary Clinton to be his secretary of state. Obama asked Rep. Steve Israel not to challenge Gillibrand, a request he honored. Just days ago, Vice President Biden called Maloney to discuss the race, a clear sign that the White House didn't want a primary fight next year.

Obama Chief of Staff Rahm Emanuel told reporters last week that the White House would help Gillibrand's re-election bid.

McKenna disputed any suggestions that Clinton is taking sides in the race, and said Clinton's attendance at past or future fundraisers should not be perceived as an endorsement.

"We agreed to this event some time ago as a way of saying 'thank you' to Congresswoman Maloney for her efforts on his wife's behalf last year," McKenna said.

Bill Clinton also did a fundraising event for Gillibrand, but word of the Maloney event comes as the congresswoman moves toward formally announcing her candidacy. An adviser said this week she is running.

Both Maloney and Gillibrand supported Hillary Clinton's failed presidential bid, and Bill Clinton had made a point of thanking supporters.

During the Democratic primaries last year, Bill Clinton publicly criticized Obama as untested and unready for the job of president. Hillary Clinton engaged in a grueling and ultimately losing battle with Obama for the party's nomination. Bill Clinton and Obama made amends and the former president campaigned for the Democratic nominee.