US Senate Majority Leader Mitch McConnell
US Senate Majority Leader Mitch McConnellReuters

Senate Majority Leader Mitch McConnell (R-Ky) has admitted that it is unlikely Congress will be able to block the Iran nuclear deal, despite a Republican majority in both houses.

The GOP senator said President Barack Obama has "a great likelihood of success" in pushing the deal through, according to AP.

While Republicans will almost certainly vote down the deal in an upcoming vote Obama has said he will use his presidential veto to override the majority vote. To cancel out that veto Congress would need a new two-thirds majority vote against, which would require a large number of Democratic congress members to join their GOP rivals.

But while some Democrats - most notably leading Democratic Senator Chuck Schumer - have indeed come out against the deal, others have voiced their support for the president.

Obama needs the support of 34 Democratic Senators, and 146 members of the House of Representatives to sustain his veto. In all, he has already received that support from 20 Senators, while in the House 48 have declared their support for the deal compared to just 10 against, with many other congressmen still not openly declaring their positions. 

Speaking to a group of American businessmen in his home state of Kentucky, McConnell admitted the likelihood of enough Democrats opposing the deal to cancel the veto is extremely slim.

"He can win by getting one-third plus one of either house, so he's still got a great likelihood of success," he said of the president.

However, he added that the next US President could review the deal.

McConnell said Republicans would universally oppose the deal, and that the President was therefore naturally focusing his lobbying efforts on members of his own party.

"The campaign of the president to get it approved will be entirely among Democrats, probably Democrats in very safe Democratic seats whose only fear of re-election would probably be getting a primary," he said.

Senator Schumer's dissenting voice was a boost to the "No" campaign, he added, but that was unlikely to be enough to defeat Obama.

"I hope we can defeat it, but the procedure is obviously stacked in the president's favor," McConnell told reporters. "We'll see."

He also welcomed news that the only Republican Senator who had been considering voting in favor of the deal, Arizona Senator Jeff Flake, had issued a statement saying he would now vote against it.

"I was pleased that he finally reached the same conclusion the rest of us did, that it was not in America's best interests to support it," McConnell said.

He warned that the deal was dangerous, and urged fellow Republicans to lead a "respectful" debate detailing its many flaws.

"It leaves the Iranians with threshold nuclear capability," he said. "It has no impact on all of their other activities. They are the biggest sponsor of terrorism in the world today. The inspections are flawed."