Senator Chuck Schumer of New York has become the first high-profile Democrat to publicly oppose the nuclear deal the U.S. and six world powers struck with Iran.

Outlining his rationale on the website Medium, Schumer said he would vote against the deal “after deep study, careful thought and considerable soul-searching.” His opposition centers on the fact Iran would be able to build a nuclear weapon after 10 years. And, Schumer says, under the deal, inspections of Iran’s nuclear sites was not “anywhere, anytime.”

Even more troubling is the fact that the U.S. cannot demand inspections unilaterally. By requiring the majority of the 8-member Joint Commission, and assuming that China, Russia, and Iran will not cooperate, inspections would require the votes of all three European members of the P5+1 as well as the EU representative. It is reasonable to fear that, once the Europeans become entangled in lucrative economic relations with Iran, they may well be inclined not to rock the boat by voting to allow inspections.

Congress has until September 17 to vote on the deal that was struck in July. President Obama has threatened a veto if lawmakers reject the historic accord. It’s unclear if opponents of the deal in Congress have enough votes to override a presidential veto.

Most Republicans oppose the deal, as does Israel. Schumer’s opposition could allow other Democrats who are privately opposed to the agreement to publicly come out against it. But my colleague James Fallows wrote this week that Schumer’s public opposition could also be good news for the deal. How?

Because it suggests that Schumer has already calculated that the administration can do without his vote.

For rococo parliamentary reasons, the crucial voting showdown is still several legislative rounds into the future. First the Congress would have to pass a measure condemning the deal, which Republican majorities in both the House and Senate will certainly do. Then President Obama would have to veto the measure, which he will certainly do. Then the Congress would have to override the veto, which requires a two-thirds majority in both chambers—and this is what the Democrats, even in their diminished numbers, should still be able to block with some votes to spare.

Several influential Democrats, including Congressman Adam Schiff of California, say they will support the agreement.

The Obama administration has made a push to promote the deal. The president called it a choice “ultimately between diplomacy and some form of war.” Secretary of State John Kerry sought to assuage Israeli concerns about the deal.