WASHINGTON (CNN) -- With the election of the next president a year away, Sen. Hillary Clinton remains the person to beat, a CNN/Opinion Research Corporation poll released Monday suggests.

As the countdown begins to November 4, 2008, the New York Democrat continues to dominate the race for the Democratic presidential nomination, and comes out ahead when voters are asked whether they prefer her or the GOP front-runner, former New York Mayor Rudy Giuliani.

But Clinton's path to the White House is in no way certain. Clinton was criticized for her performance during a debate last week, and her rivals for the Democratic nomination have stepped up attacks that she has equivocated on her position on Iraq, Iran and other major issues.

The Republican presidential candidates have also stepped up their attacks on the Democratic front-runner, with each suggesting that he has the best chance of stopping Clinton.

The attacks may be working. The CNN/Opinion Research polls suggests that Clinton's support has slipped from its height one month ago.  Watch CNN's Bill Schneider on the latest poll numbers »

"Clinton's strength is about where it was throughout the summer, indicating that she has lost the support she gained last month but that Obama has not yet cut into her core constituency," CNN political director Keating Holland said.

Clinton is the top choice of 44 percent of the likely Democratic voters interviewed for the poll. Her closest rival, Sen. Barack Obama of Illinois, was the top choice of 25 percent, and former Sen. John Edwards of North Carolina has 14 percent.

All other Democratic candidates were in single digits. New Mexico Gov. Bill Richardson was backed by 4 percent, Sen. Joe Biden of Delaware by 3 percent, Sen. Christopher Dodd by 2 percent, Ohio Rep. Dennis Kucinich by 2 percent and former Alaska Sen. Mike Gravel was at 1 percent.

The poll involved 467 interviews conducted on November 2-4 with Democrats or independents who lean Democratic. The poll's margin of error was plus or minus 4.5 percentage points.  View the poll results »

In an October CNN/Opinion Research poll, Clinton was supported by 51 percent of Democratic voters and had a 30 point lead over Obama.

During last week's Democratic debate, Clinton received heavy criticism from her fellow Democratic presidential rivals, who are desperate to shake up the presidential race just months before the first voting occurs in the Iowa Caucus in early January.

Edwards was particularly aggressive during the debate, criticizing Clinton for her stance on Iraq, Iran and Social Security.

"The American people ... deserve a president of the United States that they know will tell them the truth and won't say one thing one time and something different at a different time," Edwards said.

Edwards has also accused Clinton of being a "corporate Democrat" too willing to defend a "corrupt" Washington establishement.

"We desperately need in the next president someone that recognizes we have a system in Washington that's become broken, corruption has crept into it, and we have to tell the truth about that," Edwards said Monday. "If you defend that system, I don't believe you can bring about the change that America needs."

In the Republican presidential race, Giuliani continues to be the leading candidate, with the backing of 28 percent of the Republican primary voters polled. Former Sen. Fred Thompson of Tennessee was backed by 19 percent. Sen. John McCain of Arizona was the top pick of 16 percent, and former Massachusetts Gov. Mitt Romney had 11 percent.

Of the remaining Republican candidates, former Arkansas Gov. Mike Huckabee received 10 percent, Texas Rep. Ron Paul 5 percent, California Rep. Duncan Hunter 4 percent and Colorado Rep. Tom Tancredo 3 percent.

The poll involved telephone interviews with 397 Republicans or independents who lean Republican. The poll's margin of error was 5 percentage points.

In a head-to-head matchup of the two front-runners, Clinton leads Giuliani 51 percent to 45 percent. That lead has increased since October, when Clinton led Giuliani 49 percent to 47 percent.

"The overall political environment seems
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question: Who leads Republican presidential field, answer: Giuliani | question: Did Clinton beat Giuliani in the polls?, answer: 51 percent to 45 percent. | question: What did Clinton beat Guiliani by?, answer: 49 | question: what does this poll mean?, answer: Clinton was supported by 51 percent of Democratic voters and had a 30 point lead over Obama. | question: Who is supported  by 44 percent of Democrats polled?, answer: Sen. Hillary Clinton | question: What percent of democrats supported Clinton, answer: 44 | question: Which candidate continues to lead the Republican nomination?, answer: New York Mayor Rudy Giuliani. | question: What percentage of Democrats support Clinton?, answer: 44 percent | question: Is Clinton beating Giuliani in the polls?, answer: 51 percent to 45 percent. | question: What percentage of Democrats supports Clinton?, answer: 51 percent | question: What percent of Democrats support Clinton?, answer: 51 | question: Who leads the Republican presidential field?, answer: Giuliani | question: What percentage of democrats support Hillary Clinton?, answer: 44 percent | question: Who continues to lead?, answer: Sen. Hillary Clinton | question: what is his actual polling percent?, answer: 51 | question: What percentage of Democrats supported Clinton since October?, answer: 51 percent