Fundamental differences on foreign policy and national security, the presumed focus of tonight's scheduled debate, separate John McCain and Barack Obama.
Here's where they stand on four major challenges.
McCain, who called for ousting Saddam Hussein for years before the 2003 invasion, calls the 80 percent drop in violence “a direct result” of the 2007 surge of 30,000 extra U.S. troops and says “victory … is finally in sight.”
He opposes a timetable to end the occupation, which will cost an estimated $1 trillion-plus before it's over. He says stability and democracy can take root only if U.S. troops stay until there is political reconciliation, economic revival and Iraqi forces can operate alone.
A premature pullout, he warns, could bring renewed strife. Iraq could become a “failed state” where al-Qaida would gain a safe haven, Iran would hold sway, and violence would threaten neighboring states.
Obama, who opposed the invasion and the surge, admits the surge has worked “beyond our wildest dreams.” But he says Iraq's Shiite-led government and its sectarian rivals will put off real reconciliation unless pressured to take responsibility for their own fate by a pullout of most U.S. forces.
He vows a “responsible and phased” 16-month U.S. troop reduction that would let more U.S. forces be sent to Afghanistan, which he sees as the front line of the war on terror. His drawdown would be accompanied by initiatives on reconciliation, refugee returns and regional stability. He would leave a “residual” U.S. force in Iraq to conduct “targeted counter-terrorism missions” and protect U.S. diplomats and civilian personnel.
Most experts agree the surge reduced violence. But they note other factors: Shiite militia leader Muqtada al-Sadr declared a truce, minority Sunni Muslims had already been driven from large parts of Baghdad, and former Sunni insurgents in Anbar province had joined U.S.-funded groups to fight al-Qaida-linked extremists.
Obama says diverting U.S. troops to the “unnecessary” war in Iraq let the Taliban and al-Qaida rebuild after their 2001 defeat and establish sanctuaries in Pakistan's tribal region, where al-Qaida is plotting new terrorist attacks.
He calls Afghanistan “the war we have to win” and says he'd send thousands more troops to bolster the 72,000 U.S. and NATO forces there. He also vows to press NATO allies for more troops and would step up training of Afghan forces and non-military aid programs.
McCain, who has said the U.S. could “muddle through” in Afghanistan, disputes that rising violence is due to “our diversion to Iraq.” He would launch an Iraq-type surge to beef up U.S.-led counter-insurgency efforts. But he backtracked from a pledge to divert 14,000 troops from Iraq, now saying he would press NATO allies to provide some of the forces and equipment.
McCain would name a “czar” to oversee Afghanistan strategy, including boosting nonmilitary aid to Afghanistan and Pakistan. He also would recruit local tribes to “fight foreign terrorists,” the approach used against al-Qaida-linked terrorists in Iraq's Anbar province.
McCain, who once publicly sang “bomb, bomb, bomb – bomb, bomb Iran” to the tune of a Beach Boys song, calls it the “world's chief sponsor of terrorism” and says it seeks nuclear arms that would pose “a danger we cannot allow.”
He rejects direct talks with Tehran and would seek tighter U.N. sanctions to pressure Iran to halt its nuclear program. If that failed, he would lead “like-minded countries” in imposing sanctions, including strangling Iran's gasoline imports. He also would press for a private investment cutoff. McCain says he wants a peaceful solution, but does not rule out force.
Obama agrees “there is no greater threat” to Israel and the region than Iran. But he says he would hold direct negotiations without “self-defeating preconditions” – such as requiring Iran to first suspend uranium enrichment – and would offer incentives to halt the program and end support for terrorism. If Iran refused, he would seek tougher U.N. sanctions and work with allies on unilateral measures, including a gasoline sales ban.
Obama doesn't rule out force, but he says first exhausting all diplomatic options would ensure greater international support.
In an essay last year, McCain called for Russia's expulsion from the G-8 group of industrialized nations – which is unlikely because the other partners don't want to do it.
After the Aug. 8 Russian invasion of Georgia, he urged quick action on admitting Georgia and Ukraine to NATO. He said he told Georgian President Mikhail Saakashvili in a telephone call, “Today, we are all Georgians.”
Obama has criticized Russia's actions in Georgia and called for international peace keepers to replace Russian troops in contested regions. He favors NATO membership for Georgia in principle, but not calling to accelerate it in a time of tension. Many experts warn admission could provoke Moscow and commit the U.S. to defend Georgia in a war.