Arlen Specter’s defection to the Democratic party and the retirement of David Souter from the Supreme Court tilt the balance of power in Washington further in Barack Obama’s favour. Mr Specter has put Democrats within one vote of a filibuster-proof supermajority in the Senate, and they are likely to get that vote when Minnesota’s wrangling over last November’s election finally comes to an end. Mr Souter, meanwhile, has given the president the first of what may be several chances to define, for years to come, the character of the country’s hugely influential constitutional court.

Neither event is instantly earth-shattering. Mr Specter was an erratic Republican and is already an unreliable Democrat. Almost his first act after crossing the aisle was to vote against his new party on the budget. He complained about so-called reconciliation instructions that would let the Senate pass healthcare reform on a simple majority vote, which the administration could more easily win.