Newt Gingrich to formally end presidential campaign

Newt Gingrich is to bring a formal end to his presidential campaign and is expected to endorse the presumptive Republican nominee, Mitt Romney.

He bows out as the Obama re-election team issued a "greatest hits" video of Mr Gingrich's critiques on Mr Romney.

The former House Speaker has already thanked supporters and pledged to prevent the "genuine disaster" of Mr Obama's re-election.

Mr Gingrich end his campaign some $4m (£2.5m) in debt, according to reports.

He is expected to appear in Arlington, Virginia to formally announce the suspension of his presidential bid.

The end of his campaign leaves just Ron Paul remaining as a notional challenger to Mr Romney.

His decision also provided the Obama campaign with the opportunity to highlight Mr Gingrich's regular primary-season attacks on the man he is expected to endorse.

The edited compilation suggests Mr Gingrich does not support the Romney campaign or its key positions.

In his own video message, released on Tuesday, Mr Gingrich did not mention or endorse Mr Romney, the presumptive Republican presidential nominee.

Mr Romney and supporting groups used large numbers of negative advertisements against Mr Gingrich and fellow Republican rival Rick Santorum in the primaries.

While the former Massachusetts governor is not the official Republican nominee, he is on track to gain the 1,144 delegates needed to secure the nomination by the end of May.

Mr Gingrich's White House run was full of incident. He was largely written off in the summer of 2011 when a number of key campaign staff walked out on him.

But a series of strong debate performances brought him back to prominence, and he won the South Carolina primary in January.

He also won the primary in his home state of Georgia but failed to build further momentum during the primary season and struggled to match Mr Romney's financial muscle.