Any political party counts on having a few hot buttons it can push at  those moments when it is a few points behind in the polls with not much time till election day. These issues have certain characteristics  – a whiff of pandering, the flavour  of insincerity, an aura of  desperation. They aim to stir passion but have little, if any, effect on  most people’s lives. They are touchstones for the party’s base, but run a risk of alienating the centre. They are often symbolic or culture-war issues relating to God, country or values – though they sometimes involve race, class or economics as well. Flag-burning has long been such an issue for Republicans. Raising the minimum wage sometimes serves the same purpose for Democrats.

This week, George W. Bush smashed his party’s biggest “Break glass in case of fire” box, when he called on the Senate to pass an amendment to the constitution defining marriage as the union of a man and a woman. That Mr Bush did this, with signs pointing to a possible Democratic recapture of Congress in the autumn election, comes as no great surprise. The issue bailed him out in 2004, when state ballot initiatives on the subject helped draw evangelical voters to the polls and may have provided Mr Bush with his margin of victory in the decisive state of Ohio. But the gay marriage issue is much less likely to work for Republicans this time, for three reasons.