COLUMBIA — A new advertisement attacking likely Democratic gubernatorial nominee state Sen. Vincent Sheheen’s position in support of Medicaid expansion begins airing today in markets across South Carolina.

A political group run by supporters of Gov. Nikki Haley is responsible for the 30-second ad, which comes about 18 months before the 2014 gubernatorial election in which Haley and Sheheen are expected to square off.

The Movement Fund has spent about $300,000 so far to air the ad on both network and cable television in the Greenville-Spartanburg, Florence-Myrtle Beach and Charleston markets, said consultant Tim Pearson, who advises the group and Haley.

The ad is set to run for the first 10 days of May.

The spot claims Sheheen, a Camden Deomcrat, wants South Carolina to be the only state in the South to accept “Obamacare,” formally known as the Patient Protection and Affordable Care Act. The spot goes on to say Obamacare would raise health care costs, squeeze out private coverage and cripple state budgets. “Tell your senator to reject the Sheheen-Obamacare disaster,” the ad concludes.

In March, Sheheen said he supports a temporary expansion of Medicaid, the joint federal-state program for the needy, for the period that costs would be fully covered by the federal government.

After three years, the state would have to cover a portion of the cost of the expansion, rising to a maximum of 10 percent in 2020.

Haley’s administration has long been opposed to an expansion, and the General Assembly has so far rejected Democrats’ attempts to accept an expansion.

Another Southern Republican leader, Florida Gov. Rick Scott, has said he supports Medicaid expansion in his state. But Florida’s Legislature has thus far rejected the expansion.

Sheheen has announced a bid for governor, setting up a rematch of the 2010 race in which Haley bested him by about 4.5 percentage points.

The rollout of the anti-Sheheen ad comes on the same day the Democratic Governors Association released an online spot labeling Haley corrupt.

Read more in an upcoming edition of The Post and Courier. Reach Stephen Largen at slargen@postandcourier.com and follow him on Twitter @stephenlargen.