U.S. presidential candidates Hillary Clinton and Barack Obama waged a tight campaign fight across Ohio on Sunday as a top Democrat voiced concern about a prolonged party battle after Tuesday's voting.
Four states hold contests on Tuesday to select Democratic and Republican candidates for the November election, with Clinton and Obama focusing most of their effort on the two big states of Texas and Ohio.
Both races are very tight after Clinton held big leads a month ago, according to a Reuters/C-SPAN/Houston Chronicle poll released on Sunday.
Obama led in Texas 47 percent to 43 percent while Clinton led by a statistically insignificant one point in Ohio, 47 percent to 46 percent, the poll showed. The poll had a margin of error of 3.7 percentage points.
Obama, a senator from Illinois who would be the country's first black president, leads in the race for the 2,025 delegates needed to win the nomination at the party's summer convention. Unless Clinton wins by very big margins on Tuesday, he will pick up big chunks of additional delegates, and her future would be uncertain.
The Republican front-runner, Arizona Sen. John McCain, faces dwindling competition from the only other major Republican candidate, former Arkansas Gov. Mike Huckabee, and took the day off from the campaign trail.
A big night on Tuesday could put McCain very close to the 1,191 delegates he needs to clinch the Republican nomination.
Polls close in Ohio at 7:30 p.m. EST (12:30 a.m. British time on Wednesday) and all voting in Texas will be over at 9 p.m. EST (2:00 a.m. British time on Wednesday).
