The National Republican Senatorial Committee has purchased one week’s worth of statewide advertising for about $550,000 in Arizona to support the campaign of Rep. Jeff Flake (R). Recent polls have shown a narrowing margin between the Congressman and his Democratic rival, former Surgeon General Richard Carmona.

Politico first reported the news.

The logic in the buy, according to a national Republican, is that Flake and the groups behind him have been vastly outspent in advertising. The Club for Growth announced this week that it was spending $500,000 over two weeks in Arizona on Flake’s behalf.

But Democratic groups such as the Democratic Senatorial Campaign Committee, Majority PAC and Vote Vets have been outspending Republican groups by a 4-1 ratio in the past week.

Adding to Republican advertising woes, Carmona was also able to be on the air for much of September while Flake was dark.

There is no question that this has been a good week for Carmona. On Wednesday, his campaign announced it had raised $2.2 million in the third quarter. The Flake campaign has yet to release its own third-quarter fundraising numbers.

Roll Call rates this race as Leans Republican. This race is to fill an open-seat created by Sen. Jon Kyl’s (R) retirement.