DES MOINES, Iowa (AP) – A new television ad campaign seeks to ratchet up pressure on Iowa Sen. Charles Grassley among his constituents to accept sweeping reforms to the nation’s health care system, but even his political opponents concede there’s little that can be done to scare the veteran Republican lawmaker.

Grassley, who is among three Democrats and three Republicans on the Senate Finance Committee negotiating a health care system overhaul, has been in office since 1956 and seems set to cruise to a sixth term next year.

Democracy for America, a group founded by former Democratic National Committee Chairman Howard Dean, began running ads in Iowa on Monday that target Grassley, specifically. The ads, which are set to run through next week, argue that “when 76 percent of Americans want something done in Washington, senators like Chuck Grassley in Iowa better listen if they want to get re-elected in 2010.”

Group spokeswoman Mary Rickles said the 76 percent figure is based on a poll conducted in June by NBC News and the Wall Street Journal.

The state chapter of the AARP, Iowa’s largest seniors organization with about 400,000 members, is also lobbying Grassley to accept sweeping health care reform. But its director, Bruce Koeppl, concedes there’s little that can be done to pressure the 75-year-old senator.

“You know as well as I do that you don’t force Senator Grassley to do something he doesn’t want to do,” Koeppl said.

If Grassley is worried, he’s not showing it.

After more than 50 years in the state Legislature, U.S. House and now the Senate, Grassley has become an institution in Iowa. He has already amassed $3.8 million to use while running for a sixth term in 2010, and his potential Democratic opponents are not widely known.

“There’s nobody on either side who could seriously challenge him. He’s been such a landmark figure in Iowa politics for so long,” Drake University political science professor Dennis Goldford said.

Grassley said Monday he remains hopeful a limited health care reform measure can be negotiated, but that a small bipartisan group of senators working on the issue agrees a government-run public option won’t be part of the package. Democrats have said that while they hold out hope for a compromise, an overhaul measure will be presented this year with or without bipartisan support.

Grassley told The Associated Press he pays little attention to interest group pressure, and that his views on the health care issue hardened after he hosted a series of town hall-style meetings on the issue throughout the state.

“It’s not hard for me to conclude from my own town meetings that there’s strong opposition to a public plan,” Grassley said.

“Opposition was much stronger than what I anticipated,” he said.

Rickles dismissed the efforts of Grassley and other Republican lawmakers to seek a bipartisan plan, saying they have no intention to accept any substantive reform.

“That’s not bipartisanship, that’s choosing insurance companies over the American people,” Rickles said. “We’re just trying to make a point because Grassley is the key negotiator. There’s bipartisan support for a public option.”

But Grassley insists he’s not just going through the motions.

“Why would anybody sit in a room for four hours a day to just play a game? I’ve got more important things to do with my time,” he said.