Former Gov. Mark Sanford’s cellphone has been flooded with calls since he included his number in a full-page newspaper ad Sunday.

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He’s heard from supporters, of course, but not everyone has been friendly.

The number also was sent across the country this week via email by House Majority PAC, a Democratic-leaning Super PAC affiliated with House Democratic leader Nancy Pelosi. Sanford’s cell lit up with calls from Houston, Denver, Illinois and other states.

“I had hundreds of calls from around the United States of America,” the Republican congressional candidate said as he displayed a poster showing a sample of them. “What you have to say is, ‘Why is Nancy Pelosi working so hard in this race?’ ”

Sanford took out an ad in The Post and Courier that talked about his “rough week” since a trespassing accusation lodged against him by his ex-wife Jenny became public. He put his cellphone number in the ad and invited voters to call him if they had questions.

Sanford is locked in a battle with Democrat Elizabeth Colbert Busch for the 1st District congressional seat. The special election is May 7.

Meanwhile, Sanford picked up an endorsement Thursday from former House colleague Ron Paul.

“Mark Sanford has always been a strong ally of the Liberty Movement. Help him get to Congress. Donate today!” Paul wrote in a fundraising note.

Sanford continued to hammer at his opponent Thursday over the involvement of Pelosi and others in the race. He started the day by waving 1,000 one-dollar bills around Marion Square to decry what he called the influence of outside money, including about $400,000 from the Pelosi-affiliated PAC.

“Are we going to let folks here in South Carolina decide this race, folks here in the 1st Congressional District?” he asked. “Or are we going to let folks from outside try to buy this race?”

Colbert Busch later issued a news release that said more than two-thirds of her contributions have come from within the state, with more than 10,000 people giving an average of $63 each in the latest reporting period. Although the latest filings had yet to be published by the Federal Election Commission, the campaign said Colbert Busch pulled in $871,000 for the reporting period and has $254,000 on hand.

Earlier, she gathered with about 25 supporters in front of the West Ashley offices of the Social Security Administration to receive the backing of the National Committee to Preserve Social Security and Medicare. The committee has about 26,000 South Carolina members, including almost 4,000 in the 1st District.

Sanford was critical of the endorsement, which was announced by the group’s president and CEO, Max Richtman.

“If you look at their group ... 98 percent of all their donations and support have gone to Democrats,” Sanford said, “which I think is telling about their objectivity in this race.”

Retirement security and health care loom as pivotal issues with the likelihood of a good turnout among middle-age and older voters May 7. More than 56 percent of the district’s registered voters are 45 or older. In Beaufort County, a retiree haven, that figure climbs to 68 percent.

Both Colbert Busch and Sanford have said they believe in protecting Social Security and Medicare, at least for existing beneficiaries. But they have struck different chords as far as needed reforms.

Sanford has said the programs must be modernized for future retirees, and he often repeats this fact: The Congressional Budget Office projects that, at current rates, the federal government in 12 years will have enough income to cover only the interest on the debt and entitlements.

Colbert Busch said she opposes any effort to privatize Social Security — one of Sanford’s signature issues during his first time in Congress — but talks about the need to root out fraud and waste in Medicare, as well as the need to let the federal government negotiate lower prices from drug companies.

Richtman said Colbert Busch met with his staff in Washington, and he invited her 1st District competitors to be vetted by the group. He said Sanford declined.

“I know him (Sanford) from when he was in the Congress,” Richtman said. “There wasn’t a more active member of Congress pushing privatizing Social Security.”

The candidates’ willingness to consider privatization has emerged as a major difference.

“The governor still very much believes in letting people have ownership of some portion of their retirement and some flexibility to look for higher-yield investments,” Sanford spokesman Joel Sawyer said. “At the same time, he says any entitlement reform should not affect benefits of those currently in the system.”

Older voters tend to participate at higher rates in special elections, said Pete Jeffries of the American Association of Retired Persons. AARP doesn’t endorse candidates, but Jeffries also made the trip from Washington to Charleston this week to help distribute its voter guide.

Colbert Busch began the day in Beaufort, where Mayor Billy Keyserling endorsed her, the first time he has taken such a step.

“We need someone we can call in Washington who will pick up the phone, listen to what we have to say and help our community get stronger,” he said.

Reach Robert Behre at 937-5771.