Rep. Bill Cassidy (R-La.) (U.S. House of Representatives) Rep. Bill Cassidy (R-La.) (U.S. House Web site)

Rep. Bill Cassidy (R-La.) is running for Senate in 2014, the AP reports. Cassidy will challenge Sen. Mary Landrieu (D), a top Republican target.

In three elections, Landrieu has never won more than 52 percent of the vote, and President Obama lost Louisiana by over 17 points last fall. 

Cassidy, the first GOP candidate in the race, announced Monday that he had raised $500,000 for his likely bid. That money could scare Rep. John Fleming and former congressman Jeff Landry, potential primary rivals. Last month, Landry was openly wondering why Cassidy had not yet declared his bid and saying the delay had increased his own support.

Cassidy has also hired two well-known consultants, Jason Hebert and Scott Hobbs of the Political Firm.

Cassidy, first elected in 2008, is a doctor from Baton Rouge who founded a free community health-care clinic for working people who lack insurance.