Big voting losses bring out Clinton's stoicism

By Caren Bohan

MCALLEN, Texas (Reuters) - If Sen. Hillary Clinton fears she may be on the brink of losing her bid to become the first woman U.S. president, she is determined not to show it.

The former first lady, once the red-hot favorite, has suffered a series of big losses to her rival for the Democratic Party nomination, Sen. Barack Obama, that have rattled supporters and helped prompt a shake-up in her staff.

But though tired and battling a cough picked up during weeks of endless campaigning days, Clinton is showing much of the stoicism she displayed during her sometimes troubled years in the White House as wife to President Bill Clinton.

The New York senator has plowed ahead with a relentlessly upbeat message about the state of her campaign, brushing off the predictions of pollsters who say it is in serious trouble.

"I've heard it before. I heard it before New Hampshire and before Super Tuesday," Clinton told an ABC television affiliate on Tuesday.

"This is a close race. I'm very optimistic," she said.

She was speaking several hours before Obama's big win in three contests in the Washington D.C. area on Tuesday as he appeared to gain momentum in the close state-by-state race to represent the party in the November election.

There have been some signs that her supporters are indeed nervous and indications of some confusion in a campaign machine that had looked almost invincible last year. Some staffers have quietly acknowledged disappointment in recent results while also pressing the message that upcoming contests in Texas and Ohio will give Clinton the opportunity to rebound.