US voters are going to the polls on a crucial day of presidential primaries that could see Hillary Clinton stage a comeback or boost Barack Obama's frontrunner status in Democratic race.
Republican and Democratic primaries are being held in the states of Ohio, Vermont, Rhode Island and Texas, which also hosts a caucus later in the day.
The combined primary and caucus is a quirk of the Texas Democratic Party.
John McCain is widely expected to reach the 1,191 delegates needed to win the Republican nomination.
Senator Clinton held a rally for thousands of her supporters in Austin, Texas, last night urging them to vote in today's primary and tonight's caucus.
The campaign in Texas has seen some of the sharpest exchanges to date between Senators Clinton and Obama.
Polls show a tight race. In Ohio, an 18-point lead enjoyed by Senator Clinton three weeks ago has been whittled down to an average four-point lead in most polls.
Early voting in Texas has already been high, indicating the likelihood of a big turnout.
The Republican race is expected to be wrapped up today by Senator John McCain.
Anything less than a decisive victory on one side or the other in the Democratic race, could see it drag on into the summer.
Click here to visit the RTÉ.ie US Election website
