Republican Party Presidential candidate John McCain warned on Wednesday that Russia's invasion of Georgia was a stark reminder the world is a dangerous place and demands experience in the White House.
Senator McCain, 71, told a fund-raiser that Moscow's action was part of "the centuries' old ambitions of the Russians to establish the Russian empire."
He said "a steady hand on the tiller" was required - and "an experienced one."
President George Bush earlier announced the US military will deliver humanitarian aid to Georgia and Secretary of State Condoleezza Rice is going to Tbilisi to show "unwavering" support for the former Soviet republic.
In Russia, Foreign Minister Sergei Lavrov said Washington was playing "a dangerous game" in the Caucasus by backing Georgia.
He said the United States will have to choose between its relationship with Moscow and the Georgian leadership, which he described as a "virtual project."
However, Senator McCain said he did not envisage a return to the Cold War era.
In an interview with CNN, Georgian President Mikheil Saakashvili said both Senator McCain and Senator Barack Obama were supportive of his country, but he praised the Arizona Republican in particular.
Meanwhile, Dr Rice says Russia has "seriously overreached" itself.
She told a news conference: "This is not 1968 and the invasion of Czechoslovakia where Russia can threaten a neighbour, occupy a capital, overthrow a government and get away with it. Things have changed."