The White House and the Democratic-controlled Congress are squaring up for the next phase of what is perhaps the most bizarre political showdown of George W. Bush’s presidency.

Nancy Pelosi, speaker of the House of Representatives, will try on Thursday to override Mr Bush’s veto last month of an expansion in healthcare for impoverished children by seeking a two-thirds majority in its favour. The Senate has already approved the measure by a two-thirds majority – with considerable Republican backing.