The sole Republican Senator the Obama administration was lobbying hard to break with his party to support the president's embattled Iran deal announced Saturday that he will vote against it.

In a statement Saturday, Sen. Jeff Flake (R-AZ) dashed the hopes of the White House that he might defect from his fellow Republican Senators and provide some semblance of bipartisan support for the broadly unpopular deal.

Flake noted in his announcement that the deals contains some "benefits in terms of limiting Iran's ability to produce sufficient fissile material for a nuclear weapon for a period of time," but said ultimately "these benefits are outweighed by severe limitations the (agreement) places on Congress and future administrations in responding to Iran's non-nuclear behavior in the region."

Though the administration insists it has the ability to re-impose sanctions over bad non-nuclear behavior by Iran (like continuing to support terrorism in the region), Flake suggested that the actual terms of the deal indicate otherwise.

"Hoping that Iran's nuclear ambitions might change after a 15-year sabbatical might be a bet worth making. Believing that Iran’s regional behavior will change tomorrow - while giving up tools to deter or modify such behavior - is not," Flake stated.

Though Flake said he was in favor of the negotiation process, the specifics of the agreement made it impossible for him to back it, concluding, "I cannot vote in support of this deal."

The Obama administration reportedly put a lot of effort into courting Flake, particularly on a trip he took with the president to Africa in July, but clearly those efforts failed in light of the final "very bad" deal.

Congress will debate the "resolution of disapproval" when it returns Sept 8. Though the resolution is expected to pass, President Obama has vowed to veto Congress. He would then need only 34 votes in the Senate to block the measure.