George Perkovich, director of the Nuclear Policy Program at the Carnegie Endowment for International Peace, lambasted the bill’s congressional sponsors in Foreign Affairs. He accused the Democratic senators Robert Menendez and Charles Schumer, and the Republican senator Mark Kirk, of reckless grandstanding. “The Menendez-Kirk-Schumer bill may be politically expedient,” Perkovich wrote, “but it is also entirely unnecessary and dangerous.”

Much of the Democrats’ maneuvering is old-fashioned political posturing. All the Democratic officeholders now supporting the sanctions bill, David Weigel noted in Slate Tuesday, face tough re-election battles. Rejecting calls from the American Israel Public Affairs Committee to support the new sanctions bill could make them vulnerable to attacks of capitulating to Iran. So far, Democrats from “safer, bluer” turf—including Senators Tim Kaine and Chris Murphy—are not supporting the bill.

Ambition also plays a role here. Schumer, who is safe in New York, is looking to succeed Senator Harry Reid as majority leader. His chief rival for this job, Senator Dick Durbin, who was the senior senator from Illinois when Obama was the junior senator, is backing the administration.

Democrats who support the new sanctions bill claim that their goal is to give Obama greater leverage in talks with Tehran. But Perkovich and other experts warn that the proposed sanctions threaten to spark a tit-for-tat cycle of escalation.

As American hard-liners saber rattle, Iranian hard-liners are saber rattling back. If Congress does pass the new sanctions bill, a senior member of the Iranian parliament has threatened, his nation would respond by beginning to enrich uranium to 60 percent—a level close to that needed for a nuclear bomb.

The major unresolved issue—and the biggest threat to a comprehensive deal—is whether Iran should be allowed any enrichment capability. The White House has signaled that it would accept a tightly monitored program in Iran—one that enriches uranium only to the level used for energy and research. Israeli Prime Minister Benjamin Netanyahu and hawkish members of Congress argue that increased sanctions will force the regime to give up enrichment or collapse.

Reza Marashi, research director of the National Iranian American Council, an advocacy group that supports the nuclear talks, said it is political suicide for any Iranian official to accept no enrichment. Tehran’s hard-liners would accuse them of capitulation to the United States and Israel.

“I don’t know any Iran analyst—except for those on the far, far right,” Marashi told me in a telephone interview Tuesday, “who think that zero enrichment is possible.”

Obama has also made foreign policy missteps. As I wrote last week, the administration’s shifting positions on Syria—from demanding President Bashar al-Assad “must go” to declaring “red lines” on chemical weapons use and then backing away from military action—has hurt his credibility in the region.