A conservative super PAC is hitting Sen. Mary Landrieu for advocating for D.C. issues, a sign that her Louisiana residency will continue to be an issue this fall.

In a new video that will be distributed online, American Crossroads juxtaposes Louisiana footage from one of the Landrieu campaign's own ads with local leaders in Washington praising her work helping the city.

"The District of Columbia, which is about 650,000 people, I want to speak on their behalf," Landrieu says in the ad over an image of the Capitol dome. "I really can appreciate the life that we live on the Hill."

As an online video, the ad does not have the reach of a paid TV spot, but it is a signal of the types of arguments Landrieu's opponents will use in the closing days of the campaign. American Crossroads did not disclose how much money it will spend promoting the video.

Landrieu has recently been criticized by Republicans for not owning her own home in Louisiana, but instead claiming her parents' residence in New Orleans as her address in the state. Meanwhile, Landrieu owns a multi-million-dollar home in Capitol Hill.

In addition to American Crossroads, the pro-Republican group Americans for Prosperity has also developed an ad attacking Landrieu on residency questions.

The Louisiana Senate race is one of the most competitive in the country, with Capitol Hill publication Roll Call ranking Landrieu as the "most vulnerable senator" Tuesday.