US Vice President Joe Biden is due to face Paul Ryan, the Republican who wants that job, in their only debate later tonight.

The debate will be shown live on RTÉ News Now from 2am Irish time.

Democrats hope a good showing by Mr Biden can stop US President Barack Obama's slide in the polls after a lacklustre performance in last week's first presidential debate with Republican challenger Mitt Romney.

A Reuters/Ipsos tracking poll earlier today showed Mr Romney had extended his lead over Mr Obama to three percentage points.

In the debate Mr Biden, 69, an elder statesman and former senator, is expected to vigorously challenge the deeply conservative Mr Ryan, a 42-year-old Wisconsin congressman.

Mr Ryan is best-known as a specialist on the US budget and a drive to make deep cuts in government spending lower the deficit.

The Biden-Ryan give-and-take will engage many issues but none, polls show, is more important than the struggling economy, which has been slow to recover from the recession through nearly four years of Mr Obama's leadership and has been weighed down by persistent high unemployment.

While the Thursday night debate at a small Kentucky college is unlikely to settle the contest, it is expected to set a tone and a foundation for next Tuesday's town hall style debate between Mr Obama and Mr Romney in Hempstead, New York, in the second of three confrontations.