Republican lawmakers who don't side with a hard-line strategy threating a government shutdown this fall unless "Obamacare" is defunded should "be replaced," a former senator and head of an influential conservative think tank said Tuesday.

Jim DeMint, the South Carolina senator who stepped down earlier this week to become president of the Heritage Foundation, shrugged off the political repercussions of a potential government shutdown for the GOP.

"The risk of that is so much less than the risk to our country if we implement Obamacare," DeMint told NPR in an interview that aired Tuesday morning. "So I'm not as interested in the political futures of folks who think they might lose a showdown with the president."

And DeMint, who used a PAC during his time in office to sometimes help insurgent conservatives challenge sitting Republican incumbents in House and Senate primaries, said that Republicans who fear a showdown with President Barack Obama over his signature health care reform law should be booted from office.

"I think he [Obama] knows that Republicans are afraid," DeMint said. "And if they are, they need to be replaced."

DeMint's harsh warning toward his former colleagues in Congress is emblematic of the internal Republican strife that has made it difficult for GOP leaders in Congress to proceed with negotiations in this fall's fiscal battles. Congress must extend funding for basic government operations or risk a shutdown; lawmakers must also vote at some point to raise the limit on government borrowing to finance its existing obligations, or risk a default on the national debt.

Republican leaders have generally dismissed the strategy favored by DeMint and a handful of conservatives in Congress, which would essentially force a standoff with Obama and risk negative political fallout for the GOP in the case of a shutdown. Republican leaders have generally concluded that the strategy is unlikely to yield a major concession from Obama or Democrats who control the Senate.

Still, DeMint and Texas Sen. Ted Cruz, R, have embarked upon a bus tour with the Heritage Foundation's political arm -- Heritage Action -- intended to pressure GOP lawmakers to hold firm to the hard-line strategy before Congress returns to Washington in September.