A new poll from the National Republican Senatorial Committee shows Rep. Bill Cassidy (R) within the margin of error against Sen. Mary Landrieu (D) in the Senate race in Louisiana.

The poll, which was shared with Post Politics and conducted by GOP firm OnMessage Inc., has Landrieu at 45 percent and Cassidy at 41 percent.

The pollster, Wes Anderson, notes in a memo that Landrieu is below the 50 percent mark, which is generally considered vulnerable territory for an incumbent. Cassidy remains much less well-known than Landrieu.

Among voters who know both candidates will enough to rate them, Cassidy leads 52 percent to 41 percent.

The survey also suggests that the GOP will spend plenty of the next 15 months trying to link Landrieu to President Obama, whose approval rating in Louisiana is 37 percent. Just 33 percent of respondents favor Obama's health-care law, while 62 percent oppose it -- 53 percent strongly.

The poll included 42 percent Democrats and 40 percent Republicans. It was conducted from Aug. 13-15.

Landrieu is generally viewed as one of the most endangered incumbents facing reelection in 2014, largely because Louisiana is a very red state.

But polling of her contest has been scarce. An automated survey from GOP pollster Harper Polling in April showed Landrieu at 46 percent and Cassidy at 41 percent, while a Democratic automated poll from Public Policy Polling in February showed Landrieu leading 50 percent to 40 percent.

Another Republican is in the race, Rob Maness, but Cassidy remains the most well-known Republican in the open primary.

Update 11:50 a.m.: Another new poll, from the aforementioned Harper Polling, shows Cassidy at 47 percent and Landrieu at 45 percent.