As far as US President Barack Obama is concerned, those who continue to oppose the controversial Iran nuclear deal are "crazies."

Returning to Washington on Monday after a relaxing two-week vacation in Martha's Vineyard, Obama described himself to the media as "refreshed, renewed, recharged — a little feisty," according to Politico.

While on a limousine ride with Senate Minority Leader Harry Reid, Obama said he and his good friend talked about old times and getting back to Washington to "deal with the crazies in terms of managing some problems."

The Iran deal is being opposed by Republicans in the US Senate and House. President Obama said if the Republican-controlled US Congress succeeds in rejecting the deal, he will veto the measure.

Some Democrats are also against the deal, including Sen. Chuck Shcumer.

The President was criticised after saying that those who oppose the deal have made "common cause" with Iranian hardliners.

Reid expressed his support to the Iran deal Sunday, which may help secure its passage.

"Harry's leadership matters," Obama said of Reid's support.

During the fundraising event, Obama touted his foreign policy achievements including the Iran deal.

"And what's true here, domestically, is also true in terms of foreign policy. I mean, we've got enormous challenges around the world," he said. "But the fact is, since I came into office, not only have we been able to wind down two wars, take out bin Laden, but often without fanfare we've saved millions of lives because of initiatives to stop malaria."

He added, "We've provided billions of dollars of new initiatives to help develop the poorest countries in the world. We're promoting the education of girls and women all around the world, and championing human rights each and every day."

On the Iran deal, he said that, "we've been leaders in non-proliferation, which is part of the reason why I am so insistent that Congress not block a historic diplomatic effort when it comes to making sure that Iran does not get a nuclear weapon. And I'm so appreciative of Harry Reid's support for that effort."