...It is not just that many Democrats and even some Republicans are wary about endorsing a new American military venture. The White House is also wrestling with how to define the president’s war-making authority in a way that does not undermine his claim last year that he had finally taken the United States off a permanent war footing.

A broad authorization — like those passed after the Sept. 11, 2001, terrorist attacks and before the Iraq war — would carry echoes of the George W. Bush administration, outrage Mr. Obama’s antiwar liberal base and raise the specter of an open-ended conflict in Syria.

“For the White House, the bottom line is tailoring legal authority to match the policy objectives it shares with Congress and our allies,” said Harold H. Koh, a professor of international law at Yale. “The problem is those policy objectives vary from place to place.” (...)