BINYAMIN NETANYAHU'S speech to Congress on Tuesday will tackle some large questions of foreign policy: how to stop Iran from developing nuclear weapons, and how to manage the American-Israeli security alliance when the two countries’ governments disagree on strategies to keep Israel safe. Alas, there are several reasons to suspect that this lofty speech from Israel's prime minister is happening at this specific time and in this setting for reasons of low domestic politics, on both sides.

The timing of the speech is unusual. Mr Netanyahu is a couple of weeks away from elections in Israel, prompting opposition parties back home to call his visit to Washington essentially a campaign rally in a foreign land.

On the American side, both Democrats and some Republicans think the speech inappropriate. Mr Netanyahu—a foreign leader, albeit of a close ally—was invited to address a joint sitting of Congress by John Boehner, the Republican Speaker of the House of Representatives, to give him a platform to denounce the way that President Barack Obama is conducting nuclear talks with Iran. Mr Boehner and Mr Netanyahu planned the visit without consulting or informing the White House or State Department. Robert Kagan, a prominent conservative voice on foreign policy and no squish, called Mr Boehner’s invitation “unprecedented” in an op-ed in the Washington Post, adding that it was as if a Democratic-run Congress had invited President Jacques Chirac of France to attack the Iraq war on Capitol Hill in 2003.

Republican secrecy and the proximity of Israeli elections have allowed Mr Obama to deliver a snub dressed up as protocol. White House spokesmen explained that the president will not meet Mr Netanyahu during his visit, in line with a long-standing policy that presidents shun foreign politicians on the brink of election contests back home.

To be clear, Mr Netanyahu has every right as Israel’s prime minister to disagree with Mr Obama on the American-led multilateral talks with Iran. Indeed, several centrist Democrats worry that a flawed deal may well be in the offing, pushed by a Secretary of State, John Kerry, who puts extraordinary faith in his ability to make foes see reason, and a president who has set red lines in the past and then failed to enforce them. Tim Kaine, a Democratic senator for Virginia, joined a bipartisan group of colleagues last week in supporting a bill that would require Mr Obama to submit any Iran nuclear deal to Congress for 60 days of review, during which time most concessions would be put on hold.

But by denouncing Mr Obama in the American Congress at the invitation of a Republican House Speaker, Mr Netanyahu is gaining no new leverage in America (where he has aired his views on Iran on TV and in speeches outside Congress many times), and putting much at stake. It is telling that Mr Kaine is one of more than two dozen members of Congress who have said they will not be attending the Israeli leader’s speech. Support for Israel, which has long united both parties in Congress, is under strain.

Two overlapping beliefs explain the Republican invitation to Mr Netanyahu. First, Republicans in Congress really do believe that Mr Obama is a feckless president and terrible negotiator on America's behalf. In public and more passionately in private, senior House members and senators fret that Mr Obama does not believe in America's exceptional role as a global force for good. Instead, there is something close to a Republican consensus that the president’s worldview is steeped in the self-hating, blame-America-first moral relativism of the American left.

The second reason is that Republicans in Congress (and some Democrats) sincerely share Mr Netanyahu's sense that Mr Obama is preparing to do a dangerously bad deal with Iran, a country that cannot be trusted to keep its promises. Most agree with the Israeli leader that—with the Iranian economy reeling from sanctions and a falling oil price—this is just the moment to tighten the choke-hold and try to bring down the regime. Many Republicans are not much fussed by arguments that a tightening of sanctions now would splinter the fragile unity of the European and other world powers working with America on the Iranian talks, assuming that the Europeans, Russians and Chinese cannot be trusted anyway. As a result many Republicans are delighted to use Mr Netanyahu as an expert witness for their case against Mr Obama.

But there is a problem. If Republicans in Congress disagree with Mr Obama on how firmly to press the boot of sanctions on Iran’s neck, they are not—for all their bluster—eager to see America go to war with Iran. If Israel were to decide that it had no choice but to launch strikes against Iran, some in Congress might cheer. But what if Israel cannot inflict enough damage on Iranian nuclear sites on its own, and needs American help? Few in Congress are willing to make that case to their constituents.

In domestic debates Republicans have managed to sidestep this dilemma. It has been so profitable for them to attack Mr Obama for failing as commander-in-chief that they are rarely asked to spell out what they would do differently.

Quite a few Democrats have also played personal politics, attacking Mr Netanyahu’s visit as a breach of good manners. Senator Dianne Feinstein, a national-security hawk and Democrat from California, called the Israeli prime minister arrogant for announcing that he would speak for all Jews in his congressional address. Mrs Feinstein, who is herself Jewish, last week invited Mr Netanyahu to meet privately with members of Congress to explain his worries about Iran, but he declined.

Real policy differences lurk beneath all the shouting and mutual finger-pointing about who is insulting whom. If Mr Netanyahu suggests that the use of force may be necessary against Iran, then his fans in Congress will be in a bind. There is no war camp in Washington, of any size. And if talks do fail, then by making this a partisan argument, Mr Netanyahu has made grown-up, constructive debate in Washington that much harder.