By Gram Slattery and Alexandra Ulmer

WASHINGTON (Reuters) - The chairman of the main political action committee supporting the presidential campaign of Ron DeSantis has stepped down, according to a source familiar with the matter on Friday, in another blow to the Florida governor ahead of the first Republican nominating contests.

The resignation of Adam Laxalt from the Never Back Down super PAC, first reported by The New York Times, comes just more than a week after the exit of the super PAC's chief executive, Chris Jankowski, and as DeSantis struggles to hold onto his No. 2 standing in the Republican contest.

Laxalt's resignation is significant because Never Back Down has been playing an unusually prominent role in DeSantis' campaign. Super PACs can receive donations of unlimited size, but cannot coordinate directly with campaigns.

Laxalt did not immediately respond to a request for comment, nor did DeSantis' campaign.

The Times reported that Laxalt wrote in a letter to Never Back Down's board that he needed to dedicate more time to his family and his law practice.

However, one source with knowledge of Laxalt's thinking said Laxalt was concerned about what he saw as excessive spending at the group.

Nikki Haley, a former U.S. ambassador to the UN and former South Carolina governor, has surpassed DeSantis in some of the states that play the most pivotal role in the Republican primaries. Both DeSantis and Haley are more than 40 points behind former President Donald Trump, the Republican frontrunner in most national polls.

The Iowa Republican caucuses on Jan. 15 will kick off the presidential nominating contests.

(Reporting by Gram Slattery and Alexandra Ulmer; editing by Ross Colvin and Leslie Adler)