Democrats on the Senate foreign relations committee will on Thursday make a final attempt to persuade their Republican colleagues to block the nomination of John Bolton for US ambassador to the United Nations.

The stakes in the Bolton debate, which has become one of the most abrasive battles during President George W. Bush's second term, are high for a president who claimed that his re-election gave him political capital to spend. The White House is keen to avoid a repeat of last month when George Voinovich, an Ohio Republican, sided with the Democrats to postpone a vote on Mr Bolton's nomination