The white smoke that wafted out of the chimney Tuesday at Palais Coburg in Vienna signaled the start of an intense lobbying campaign on Capitol Hill over the fate of the Iranian nuclear agreement, pitting against each other two longtime adversaries, President Barack Obama and Prime Minister Benjamin Netanyahu.A primary object of their attention will be Sen. Chuck Schumer, the man who claims the title “Shomer Yisrael,” guardian of Israel, and wants to be the next Senate Democratic leader. The challenge facing the Brooklyn Democrat is how to retain both titles.Although an outspoken critic of Iran and advocate of tough sanctions, he has been careful not to tip his hand, insisting he wants to see the details of the agreement before making any commitment – an uncommon example of statesmanship in an environment in which most Republicans will automatically oppose any agreement that wears Obama’s imprint.Schumer, now number three in the Senate Democratic hierarchy, is the chosen (and presumptive) successor to retiring leader Harry Reid of Nevada.Many of his colleagues, not just the undecided, will be watching to see what Schumer does. He will be the canary in the coal mine who will give the first signals as to whether the deal can survive or will quickly run out of air.He will be watched for his dual roles as a party and Jewish leader – he has boasted of being Netanyahu’s best friend on Capitol Hill. As he goes on the Iran agreement many of his Democratic colleagues are likely to follow, knowing they have the cover of their next leader and a pro-Israel shtarker with nearly 1.8 million Jewish constituents.Schumer is already under intense pressure from Jewish organizations and machers, particularly on the Right. He is the top target of a multi-million-dollar ad and lobbying campaign urging his constituents to tell him to vote no. The American Israel Public Affairs Committee, the well-funded lobby group that has led the anti-Iran movement for more than two decades and is close to Netanyahu and Congressional Republicans, is leading the campaign against the Iran agreement. It has mobilized its members, particularly major political contributors, to personally pressure lawmakers to oppose the deal.Their strategy is to set the bar unrealistically high and then insist the deal should be scrapped unless it meets AIPAC’s five demands: unimpeded “anytime, anywhere” inspections, including military facilities; full disclosure of prior weaponization efforts; no sanction relief until Iran has complied with its commitments; “decades” long term of agreement and inspections, and dismantling of Iran’s nuclear infrastructure.These are essentially Netanyahu’s terms as well, and they are shared by other opponents of the agreement.They have names like the American Security Initiative, the Emergency Committee for Israel, a creation of Bill Kristol, a Republican neocon who is often to the right of even Netanyahu; the Israel Project, run by former AIPAC spokesman Josh Block; Secure America Now, a Tea Party affiliate, and Christians United for Israel.Weighing in on the Left will be Americans for Peace Now and J Street, the pro-peace lobby. They are much smaller but have one advantage: they more closely reflect the views of the broader Jewish community.A national survey of 1,000 American Jews for J Street last month showed 59 percent supported a compromise agreement; that’s higher than the 53% of the general US population when CNN asked the identical question.The primary lobbying target will be legislators up for reelection next year, particularly Jews and Democrats.Actually, they won’t be voting on the actual agreement. Once the pact is signed it must be sent to Congress, which will have 60 days to decide whether to permit the president to waive or suspend congressionally mandated sanctions. It can vote for a resolution to disapprove, approve or take no action. In the latter two cases, the president would be free to act as he wished.Republicans are expected to vote almost unanimously against Obama’s major foreign policy initiative, not on the merits of the agreement but out of spite and politics. So look for resolutions of disapproval to easily pass both chambers because Republicans have majorities.The president will veto the resolution and he will need only one third plus one of the votes in either chamber to sustain his veto. The primary target will be the Senate, where Obama will need 34 of the 46 Democrats, assuming Republicans vote en bloc.And that’s why Schumer’s vote is so critical. He has called this one of the toughest decisions he’s ever had to make. He will face enormous pressure from the White House, from his friend Netanyahu, from pro-Likud Jewish organizations and from single-issue pro-Israel Jewish political donors.Schumer hasn’t hesitated to criticize the administration’s approach to Iran or to support toughening sanctions, but that doesn’t mean he shares Netanyahu’s enthusiasm for a military strike, calling it the “next worst” option to Tehran actually getting the bomb.If he joins the opposition and brings down the president’s Iran deal, he can give cover to Democrats who want to vote against it, but that is highly likely to endanger his chances of becoming Senate Democratic leader.Leading pro-Israel Democrats on the AIPAC-led opposition’s target list include Rep. Nita Lowey of New York, the ranking member of the appropriations committee; Sen. Ben Cardin of Maryland, ranking member of Senate Foreign Relations Committee; Rep. Debbie Wasserman Schultz of Florida, chair of the Democratic National Committee who represents a very hawkish Jewish constituency; Rep. Steny Hoyer of Maryland, number two in the House Democratic leadership, and Senators Richard Blumenthal of Connecticut, Michael Bennett of Colorado, John Tester of Montana and Chris Coons of Delaware. All but Hoyer, Tester and Coons are Jews.While Netanyahu and his supporters attack the agreement as a threat to the survival of the Jewish people, senior Israeli military and security officials are privately telling Israeli media outlets a very different story. Reuters reported the generals are saying intensified international inspections of Iran’s nuclear facilities and scaling back of its uranium enrichment will “allow for the supposition that, in the coming period of years, this is a threat in decline.” You can expect the Pentagon to share this assessment with its friends on the Hill.The saddest part of all this is that what should be a vigorous debate on the merits of a very complex diplomatic initiative will instead be mostly a highly partisan food fight. Sen. Schumer, with his unique qualifications, is one of very few lawmakers who can steer it in a more productive direction.