President Obama conceded Wednesday that lifting economic sanctions on Iran will boost that country's economy and let it funnel more money to Hezbollah and other terrorist groups, but said the only real alternative would still present Tehran with a windfall of cash, and reduce U.S. influence over its nuclear program.

"Do we think that with the sanctions coming down, that Iran will have some additional resources for its military and for some of the activities in the region that are a threat to us and a threat to our allies?" Obama said at the White House in response to a question about the Iran nuclear deal. "I think that is a likelihood, that they've got some additional resources."

Obama then tried to downplay that possibility. "Do I think it's a game-changer for them? No," he said.

He also said keeping nuclear weapons away from Iran will make it "a lot easier for us to check Iran's nefarious activities."

Republicans have said sanctions are the only tool that forced Iran to negotiate at all, and should be leaned on in the wake of the nuclear agreement they oppose. But Obama said the notion that the U.S. can keep existing sanctions in place with the same effectiveness is "not true, that is absolutely not true."

Economic sanctions require the cooperation of other countries, "many of whom really want to purchase oil from Iran," Obama said. Going along with U.S.-led sanctions thus far has cost those countries "billions of dollars" — a price they were willing to pay "because they believe we were sincere" about reining in Iran's nuclear program diplomatically.

But now, if Congress vetoes the deal, "the sanctions system unravels," Obama said, because other countries aren't supporting it anymore. He said U.S. sanctions on their own wouldn't take a big enough bite out of Iran's bottom line to affect its behavior.

"So maybe they don't get $100 billion; maybe they get $60 billion or $70 billion instead," Obama theorized if the U.S. stood alone in continuing to sanction Iran. "The price for that, that we've paid, is that now Iran is pursuing a nuclear weapon. We have no inspectors on the ground. We don't know what's going on. They're still getting some cash windfall … a terrible position [for the U.S.] to be in."

Obama also tried to downplay the idea of Iran funding terror, by saying Iranian President Hassan Rouhani has to spend some of the estimated $100 billion in new revenue domestically.

The six world powers that negotiated the deal with Tehran know that Iran won't "just spend it on daycare centers and roads and paying down debt." Obama said. But "we think that they have to do some of that, because Rouhani was elected specifically on the premise of improving the economic situation inside of Iran."

"So the notion that they're just immediately going to turn over $100 billion to the IRGC or the Quds Force, I think runs contrary to all the intelligence that we've seen and the commitments that the Iranian government has made," he said, referring to Iran's Revolutionary Guard and its elite unit that operates outside of Iran.