President Bush (search) sought to rally U.S. troops in Iraq ahead of Saturday's vote on new constitution and to brace them for an expected surge in violence, saying "the enemy understands that a free Iraq would be a blow to their vision."

"We put in motion something that can't be stopped, and that is the march of freedom," Bush said Thursday in a video conference with soldiers from the Army's 42nd Infantry Division, based in Tikrit, hometown of deposed Iraqi leader Saddam Hussein (search).

Bush spoke two days before Iraqis vote on a new constitution. A compromise endorsed on Wednesday by the Iraqi parliament made key concessions to minority Sunni Arabs, increasing the chances that the document will be approved. Passage of the constitution would open the way to national elections in December.

"We're never going to back down, we're never going to give in, we'll never accept anything less than total victory," Bush said. "Thank you for all your work. When you get back to the United States, if I'm hanging around, come by and say hello."

The president engaged in a question and answer session with 10 American servicemen and women and one Iraqi soldier, whom he saw on a large video screen set up in a room of the Eisenhower Executive Office Building next to the White House.

"Do the Iraqis want to fight, and are they capable of fighting?" he asked. He was told they were.

"The Iraqi army and police services, along with coalition support, have conducted many and multiple exercises and rehearsals," Capt. Stephen Pratt (search) of Pocatello, Idaho, told Bush. "Along with the coalition backing them, we'll have a very successful and effective referendum vote."

1st Lt. Gregg Murphy (search) told the president that at last January's elections to select an interim government, "We had to lead the way. This time, they're doing everything. ... They've got it laid out."

While polls show declining support for the war, Bush told the soldiers: "You've got to know, the American people are standing strong with you," Bush said.

The exchange was carefully choreographed.

Before it began, a Pentagon official coached the troops, telling them the president planned to ask questions on three topics: The overall security in Iraq, how they were preparing for the vote on Saturday and how much progress had been made in the training of Iraqi troops.

Allison Barber, a Pentagon official, said Bush would ask them specifically, "In the last 10 months, what kind of progress have we seen?"

She asked who was prepared to answer the question. "Master Sgt. Lombardo," one said.

After Bush asked just that question, Master Sgt. Corine Lombardo (search) responded: "Over the past 10 months, the capabilities of the Iraqi security forces are improving ... They continue to develop and grow into a sustainable force."

Bush said that the United States and its allies are facing "an enemy that actually has a philosophy."

"And the philosophy is so opposite of ours. It is the exact opposite of what America stands for. We stand for religious freedom and freedom to speak and women's rights and capacity for people to realize their dreams.

"We are facing an enemy that is ruthless and cold blooded," Bush said.

U.S. officials have predicted a spike in violence ahead of Saturday's vote.