WASHINGTON (CNN) -- The sharp differences between the Democratic and Republican presidential candidates over the war in Iraq shared the spotlight Tuesday during Senate hearings.
Sen. Barack Obama called the invasion of Iraq a "massive strategic blunder" at Senate hearings Tuesday.
Sen. John McCain, the presumptive Republican presidential nominee, said that success in Iraq was "within reach" at the beginning of the high-profile hearing on Iraq involving Gen. David Petraeus, the top U.S. general in Iraq, and Ambassador to Iraq Ryan Crocker, the top American diplomat in Baghdad.
"Our goal -- my goal -- is an Iraq that no longer needs American troops, and I believe we can achieve that goal, perhaps sooner than many imagine," McCain said.
"But I also believe that the promise of withdrawal of our forces regardless of the consequences would constitute a failure of political and moral leadership."
"Success -- the establishment of peaceful, democratic state, the defeat of terrorism -- this success is within reach," he said. "Congress must not choose to lose in Iraq. We must choose to succeed."
In apparent response to McCain, Sen. Hillary Clinton said Tuesday that the opposite was true: It would be "irresponsible" to continue a failed policy in Iraq. Watch the candidates take part in the hearings »
She said it was "time to begin an orderly process of withdrawing our troops" from Iraq in order to focus on Afghanistan and other U.S. interests.
"It might well be irresponsible to continue the policy that has not produced results that have been promised time and time again," she said, noting a "lack of political progress over the past six months" in Iraq.
And Sen. Barack Obama, a member of the Foreign Relations Committee, questioned whether the conditions set by U.S. commanders for withdrawal would lead to a war that could last 20 to 30 years.
He called the invasion of Iraq a "massive strategic blunder" that enabled al Qaeda and Iran to spread their influence into Iraq, and he said the United States should pressure Iraqi officials to settle the war by threatening to leave.
"Nobody's asking for a precipitous withdrawal. But I do think it has to be a measured, but increased, pressure and a diplomatic surge that includes Iran," Obama said. "Because if [Prime Minister Nuri al-Maliki] can tolerate normal neighbor-to-neighbor relations in Iran, then we should be talking to them as well. I do not believe we're going to be able to stabilize the situation without them."
Iraq's ambassador to the United States said Tuesday that the United States has to keep its forces in his country unless it wants Iran to have a free hand in Iraq.
McCain, Clinton and Obama questioned Petraeus and Crocker during their appearance before the Senate Armed Services Committee on Tuesday. McCain is the committee's top Republican. Watch McCain warn against a "reckless" withdrawal »
Before the hearings began, Obama and Clinton took to the airwaves to criticize McCain for supporting a long-term deployment of U.S. troops in Iraq. Watch how campaign politics influenced today's hearing »
"The problem is that there is no end in sight because John McCain has not offered any clear point at which he suggests it's time for us to move our troops home," Obama told NBC on Tuesday.
"At some point, we have to say to ourselves that the Iraqi government has to stand up and make the difference," he added.
Both Clinton and Obama have said they would begin withdrawing combat brigades from Iraq almost immediately after taking office.
"A year from now, if I'm the president, we're going to begin ending American military involvement in Iraq," Clinton said Tuesday. "I think that's the right decision for America, for our military and for the Iraqis who have to come to grips with the fact that it's up to them to decide how to use the freedom that they've been given.
"We cannot impose a military solution and that's obvious. There doesn't seem to be much evidence that they're willing to take that responsibility, and I don't think they should get a blank check from the United States any longer," she added.
In his statement, Petraeus told the Senate Armed Services Committee that he recommends allowing American troop levels in Iraq to fall to their pre-surge levels this summer.
Petraeus said the military should then pause for 45 days before deciding on the appropriate troop level.
On the political side, Crocker pointed to slow but steady political progress in Iraq.
Crocker also argued that al-Maliki is making more of an effort to work with Iraq's various factions and political parties.
The ambassador brought up meddling by Iran and called for greater participation by Iraq's Arab neighbors. E-mail to a friend