Two Veterans Groups, Left and Right, Join Forces Against the Forever Wars

“The Koch network has invested substantially in advancing their foreign policy vision over the past few years,” Mr. Caldwell said, adding of his group: “When we engage on an issue, we do it in a way where we can make the most impact. Also, one thing we will be weighing more heavily when considering supporting candidates is their alignment with us on foreign policy.”

Representative Eliot L. Engel, Democrat of New York and the chairman of the House Committee on Foreign Affairs, has been slowly seeking to build consensus among Democrats around the contentious issue by pushing measures like the one to end American military aid to Saudi Arabia.

“Congress has constitutional authority over war powers, but for too long, we’ve ceded that responsibility to the executive branch,” he said. “I’m working to reclaim our prerogatives and increase transparency about American military involvement.”

Public support for Congress asserting its authority in war powers would be “very meaningful to members,” said one Democratic aide, when told of the alliance between the two veterans organizations.

Senator Jim Risch, Republican of Idaho and the chairman of the Senate Foreign Relations Committee, has been an ally of the Trump administration, which has opposed new authorization measures.

But he said that may come before his committee anyway. “We may get there,” he said, calling war authorization “one of the most interesting yet vexing issues” he has seen in his entire public service career. “I would love someone to come up with a silver bullet,” he said.

In the meantime, the two veterans organizations, which took opposite sides in expensive and bruising Senate battles last year, will continue to try to destroy each other outside these matters.

“We might disagree on 99 percent of things,” Mr. Soltz said, “but if we agree to get that one perfect thing done, we have credibility because of our work on those other issues.”