In order to garner Democratic lawmakers to support the U.S.-Iran nuclear deal, President Barack Obama wrote a letter to Congress promising that the U.S. would take military action to ensure that Iran upholds its end of the bargain.

Under the historic deal, which Obama announced last month, the U.S. and four other major world powers agreed to lift Iran's economic sanctions. In turn, the Islamic republic vowed to limit its nuclear program for the next 10 years.

Critics, however, argued that Iran cannot be trusted and will likely continue to build nuclear warfare once the sanctions are lifted. The majority of Republican leaders in the House and Senate have also promised to disapprove the nuclear deal once the resolution is presented for a vote in mid-September.

To guarantee that the deal is approved by Congress, the president launched a campaign in July to rally Democratic support. He also told Congress in his letter that the U.S. will "take whatever means are necessary" to enforce the agreement and prevent Tehran from building nuclear weapons.

"Should Iran seek to dash toward a nuclear weapon, all of the options available to the United States -- including the military option -- will remain available through the life of the deal and beyond," Obama said in a letter, which was released by the White House on Thursday, according to  The New York Times.

In his letter, which was addressed to Democratic Rep. Jerrold Nadler of New York, Obama said the U.S. and allies are prepared to "snap back" economic sanctions if Iran fails to live up to the terms of the agreement, reports USA Today.

"In fact, we have a wide range of unilateral and multilateral responses that we can employ should Iran fail to meet its commitments," Obama wrote.

Nonetheless, some members of Obama's party, like high ranking Democratic Sen. Chuck Schumer of New York and Sen. Bob Menenez of New Jersey, have promised to vote against the deal.