President Obama is only backing the Gang of Six deficit-reduction proposal because Republicans are on the offensive with a plan of their own, Sen. Jim DeMint (R-S.C.) said.

"I don't know enough about the Gang of Six proposal, but I do know the only reason the president is stepping up and saying he might support this is that Republicans are now on the offense with a plan that would increase the debt limit in a way that Moody's and S&P would recognize as credible long-term deficit reduction," DeMint said Tuesday on Fox Business Network.

Earlier on Tuesday, Obama voiced his support for the $3.7 trillion deficit-reduction proposal the so-called "Gang of Six" group of senators unveiled.

DeMint reiterated support for House Republicans' "cut, cap and balance" bill, which would raise the debt ceiling by $2.4 trillion, but would implement $111 billion in spending cuts and a yearly cap on federal spending and require Congress to approve a balanced-budget amendment.

"There is only one proposal that actually is written that will be voted on, and that is the ‘cut, cap and balance’ proposal," DeMint said.

The Republican-controlled House is scheduled to vote on the conservative plan Tuesday evening. It is expected to pass before being defeated in the Senate.

Obama praised the Gang of Six plan as "broadly consistent with the approach I've urged." 

In praising the plan, the president joined a growing number of legislators in support of the proposal.

Sen. Tom Coburn (R-Okla.), who rejoined the Gang of Six, hailed the group's plan as something that could make it through the Senate.

"This doesn’t solve our problems, but it creates the way forward where we can solve our problems," Coburn said.