President George W Bush has accepted that the surge in violence in Iraq may be equivalent to America's traumatic experience in the Vietnam War.
Mr Bush told ABC News that it could be right to compare Iraq's situation to the 1968 Tet offensive, widely seen as a key turning point in the conflict.
But he denied that the rising number of Iraqi and US military deaths meant the Iraq campaign was failing.
October is on course to be one of the bloodiest months for US forces in Iraq.
So far about 70 troops have died, and with an average of three Americans dying every day this is one of the highest casualty rates sustained by the US military since January 2005.
In an interview with ABC News, Mr Bush was asked if he agreed with a newspaper columnist who had written that the current fighting in Iraq may be compared to the Tet offensive in Vietnam.
Launched on 31 January 1968 - Tet holiday - by North Vietnamese Army and Vietcong
Five major cities and 36 provincial capitals attacked simultaneously
Onslaught surprises US troops, is quickly repelled
US public opinion turns against the war
President Johnson's popularity falls
He withdraws as candidate for re-election in March
"He could be right," Mr Bush said. "There's certainly a stepped up level of violence and we're heading into an election."
During the Tet offensive, the Viet Cong and North Vietnamese armies launched a combined assault on US positions.
Militarily, the assault failed but it was a huge psychological blow for the Americans and their allies, and eroded political support for the then president, Lyndon Johnson.
Mr Bush appeared to suggest that steadiness of nerve could avoid a repeat of history, says the BBC's Justin Webb in Washington, although any comparison with Vietnam raises eyebrows in the US.
The White House later sought to clarify Mr Bush's comments.
"The full context was that the comparison was about the propaganda waged in the Tet Offensive...and the president was reiterating something he's said before - that the enemy is trying to shake our will," spokeswoman Dana Perino said in a statement.
In the interview, Mr Bush reiterated that US troops would stay despite the casualties.
"Al-Qaeda is still very active in Iraq...They are trying not only to kill American troops but they're trying to foment sectarian violence. They believe that if they can create enough chaos, the American people will grow sick and tired of the Iraqi effort and will cause (the) government to withdraw."
With the latest opinion polls suggesting that Mr Bush's Republican Party faces defeat in next month's mid-term congressional elections, the president is doing his best to fight his corner, our correspondent says.
The enemy defined success or failure by the number of casualties, Mr Bush said.
His definition was whether Iraqis could defend themselves, whether schools were being built, hospitals being opened.
"I define success or failure as whether we're seeing a democracy grow in the heart of the Middle East."
Pulling out troops from Iraq would be the equivalent of surrender, he said.
"I'm patient. I'm not patient forever...But I recognise the degree of difficulty of the task, and therefore say to the American people we won't cut and run."