President Barack Obama was presented with a timely 99th-day political windfall on Tuesday when Republican lawmaker Arlen Specter switched parties, giving the administration the prospect of a filibuster-proof 60-seat majority in the US Senate.

The move by the 79-year-old from Pennsylvania, who faced a tough Republican nomination battle next year, will strengthen the White House’s domination of the political agenda by giving Democrats on Capitol Hill sufficient votes to marginalise the increasingly obstructionist Republican opposition.