But it was Obama who collected a key labour union endorsement on Friday. At the same time he criticised his rival for supporting legislation harmful to workers such as the North American Free Trade Agreement.
In the Republican race, John McCain, the party’s presumptive nominee, was to receive an endorsement from former President George W Bush on Monday, Republican officials said.

The officials spoke on Friday on condition of anonymity.  The former president’s endorsement, which follows one from ex-Florida Governor Jeb Bush, is a further nudge by Republican chieftains for conservative activists to get over their distaste for McCain and for former Arkansas Governor Mike Huckabee to quit the race.
As he took a commanding lead in the delegate count, McCain has been working to solidify his support from a Republican base, unhappy with his unorthodox positions on some tax cuts, immigration, campaign finance laws, global warming and stem cell research.

On Thursday, former Massachusetts Governor Mitt Romney asked his national convention delegates to swing behind the veteran Arizona senator and former Vietnam prisoner-of-war.
The additional delegates, assuming they all choose to back McCain, would put him just 63 shy of the 1,191 needed to clinch the party’s nomination at this summer’s convention in St Paul, Minnesota.