Senator Mary Landrieu Senator Mary Landrieu (D-LA) (Melina Mara/The Washington Post)

That Sen. Mary Landrieu (D-La.) is among the most vulnerable Democrats is a problem all of her own making. Though she represents a very red state, her record is far more liberal. Landrieu has voted for the Obama stimulus, Obamacare, tax hikes, the most anti-defense nominee in history to head the Pentagon and most recently the ludicrous Senate budget that several of her moderate colleagues were smart enough to oppose.

No wonder the Republican National Senate Committee is blasting out an email citing the New York Times for the proposition Obamacare can’t deliver on its promised benefits for small businesses: “Unable to meet tight deadlines in the new health care law,” the Times writes, “the Obama administration is delaying parts of a program intended to provide affordable health insurance to small businesses and their employees — a major selling point for the health care legislation.” Even more mindboggling was Landrieu’s vote against repeal of the unpopular Obamacare medical device tax, which 79 of her Senate colleagues favored.

Today she got word yet another GOP challenger, Rep. Bill Cassidy (R-La.), will enter the race to oust her. The Hill reports: “Cassidy has been preparing for a run behind the scenes for the past few months, and announced on Monday that he raised more than $500,000 in the first quarter of this year, a strong haul for a Senate candidate this early in the cycle. He’s been traveling to events outside his district and recently signed up prominent Louisiana consultants Jason Herbert and Scott Hobbs to help.”

For election after election, red-state Democrats have talked a good game back home but voted with the liberal national Democratic leadership whenever it mattered. Landrieu just has been less skilled than others in concealing that chasm between her home state posturing and her voting record.

This Senate race is virtually a do or die for Republicans. If they can’t show voters how a pol like Landrieu has morphed from a Louisiana moderate into a Beltway liberal, they might as well close up shop. The party better start early in its assault and come up with a bullet-proof opponent or she will slide through once again on her wildly disingenuous claim to represent the views of her constituents.