Sen. Joe Donnelly, D-Ind., said he supports President Barack Obama’s proposed agreement with Iran to limit that nation’s nuclear power capabilities.

Donnelly said in a statement Wednesday that he worries about a possible U.S.-Iran war as early as next year without the accord.

As a Democrat from a largely Republican state, Donnelly had been considered a possible swing vote when the Senate and House consider a resolution to disapprove of the Iran nuclear deal next month. But he squelched that speculation with his four-paragraph statement.

“With or without this deal, the day may come when we are left with no alternative but to take military action to prevent Iran from crossing the nuclear threshold,” said Donnelly, a member of the Senate Armed Services Committee.

But he also said, “I owe it to the men and women of our Armed Forces and to the people of Indiana to have exhausted every other option to stop Iran before we would consider putting any of our servicemembers in harm’s way.”

Donnelly said he is “willing to give this agreement the opportunity to succeed. While I share the concerns expressed by the agreement’s critics about what may happen 10, 15, or 20 years from now, I cannot in good conscience take action that would shift the potential risks of 2026 and 2031 to 2016.”

The U.S. and five other world powers propose ending economic sanctions against Iran if it restricts its uranium enrichment for the next 15 years to a level that cannot be used to build nuclear weapons.

Obama warned in July that either the diplomatic agreement or a likely U.S.-Iran war “are the options,” and he pledged to veto any legislation that would block the agreement. Donnelly’s backing gives the White House another vote if the GOP-controlled Senate tries to override a presidential veto.

Many congressional Republicans, including Sen. Dan Coats, R-Ind., have indicated that they will vote to reject the agreement. Only two Democratic senators – Chuck Schumer of New York and Robert Menendez of New Jersey – have said they will oppose the deal.

Coats wrote a column in July in which he contended that negotiators had produced “an agreement with benefits too small, a duration too short and a cost too high.” He called it a “bad deal.”

Rep. Marlin Stutzman, R-3rd, last month said he was disappointed that the agreement would allow Iran to continue uranium-enrichment activities, although he stopped short of opposing it. Stutzman instead called on his colleagues “to determine what this deal buys us and at what cost while finding a resolution that protects the United States of America.”

Donnelly’s statement described a nuclear-armed Iran as “an unacceptable threat,” and he complained that the U.S. has “done too little for too long to cut off Iran’s support for terrorists and other proxies” in the Middle East.

“It is time for the U.S. to lead our allies in a clear and decisive strategy to push back against Iran’s actions,” he said.

By Journal Gazette