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(CNN) -- As President Obama prepares to unveil his long-awaited strategy for Afghanistan, key members of his own party warn that he's facing a tough sell.
The president is expected to lay out his plans for the 8-year-old war Tuesday night at the United States Military Academy in West Point, New York.
Obama's announcement is expected to include a significant boost in troop levels. The Pentagon is making plans to send about 34,000 more U.S. troops to Afghanistan in anticipation of Obama's decision, a defense official said.
Democrats say Obama must strike a difficult balance, convincing the public that sending more troops is the right thing to do in order to get out of Afghanistan as soon as possible.
"I think he has to make a speech that shows that all of our efforts are pointed to our reduced presence in Afghanistan, but I think he has to also indicate again and again how critical this is to our national security," Democratic Sen. Jack Reed, a member of the Senate Armed Services Committee and a West Point graduate, told CNN's "State of the Union."
Reed said he will support the president as long as he explains how adding more troops would allow the United States to eventually shift operations to the Afghan people.
Obama will explain Tuesday why the United States is in Afghanistan, its interests there and his decision-making process, but "the president does not see this as an open-ended engagement," White House Press Secretary Robert Gibbs said.
Republican strategist and CNN contributor Ed Rollins said Obama will have to address some key questions from within his own party.
"There has to be real clarity. Why are we there? How long are we going to be there? And equally as important, what is the mission and how is the mission different now than it was two years ago or four years ago?" Rollins said.
"Democrats have to be convinced. The president's party is certainly very divided on this issue. I think he'll have the Republican support he needs, but at the end of day, if this is not a bipartisan effort, long-term, they won't get the resources and the funding to make it work," he said.
The president ordered more than 20,000 additional troops to Afghanistan in March. Gen. Stanley McChrystal, the top U.S. commander in Afghanistan, reportedly has called for up to 40,000 more to wage a counterinsurgency campaign against the Taliban, the Islamic militia originally ousted by U.S. military action in 2001.
About 68,000 U.S. troops are in Afghanistan, along with about 45,000 from the NATO alliance.
Democratic strategist and CNN contributor Donna Brazile said Obama needs to explain what has changed since he first laid out his strategy for the region.
"I think the president needs to update us on what has occurred since March that requires to send more troops, more civilians, and how will this be different than, say, what it was two years ago or even in the near future?
"So I think this is a very important speech to not just convince the left but to convince the country that this is an important use of our resources," she said.
The cost of the war has been a sticking point for Democrats. House Speaker Nancy Pelosi cautioned last week, "There is serious unrest in our caucus about, 'Can we afford this war?' "
Prominent Democrats close to Pelosi, including House Appropriations Chairman David Obey, are proposing to pay for the way with an increase in income taxes for all Americans, except military families. Senate Armed Services Chairman Carl Levin is proposing a similar tax, but only for wealthy Americans.
"My point and our point is simply that, in this war, we have not had any sense of shared sacrifice. The only people being asked to sacrifice are military families," Obey said.
"I'm very dubious about this whole effort in Afghanistan and Pakistan, but if we're going to do it, we shouldn't do it in a way which will destroy every other initiative that we have to rebuild our own economy," he said.
Vermont Sen. Bernard Sanders, an independent who caucuses with the Democrats, says he has concerns about sending more troops to Afghanistan, given the cost.
"I've got a real problem about expanding this war where the rest of the world is sitting around and saying, isn't it a nice thing that the taxpayers of the United States and the U.S. military are doing the work that the rest of the world should be doing?" he said on ABC's "This Week."
"So what I want to see is some real international cooperation, not just from Europe but from Russia and from China," he said.
Critics of the war have also expressed concerns about the legitimacy of the Afghan government. Afghan President Hamid Karzai won another term in office this month after his opponent for the runoff withdrew.
Sen. Paul Kirk Jr., D-Massachusetts, explained in an opinion piece in The Boston Globe why he opposes a troop increase.
"Without a legitimate and credible Afghan partner, that counterinsurgency strategy is fundamentally flawed. The current Afghan government is neither legitimate nor credible," he said.
"We should not send a single additional dollar in aid or add a single American serviceman or woman to the 68,000 already courageously deployed in Afghanistan until we see a meaningful move by the Karzai regime to root out its corruption," he added.
Obama, he said, has "inherited no good options, but a more focused strategy with no additional troops stands out as preferable to all the others."
Americans are divided over the best way forward in Afghanistan, according to a CNN/Opinion Research Corp. survey released last week.
Half of the people questioned said they would support a decision by Obama to send an additional 34,000 troops to Afghanistan, while 49 percent were opposed.
The survey indicates that 52 percent oppose the war, compared with the 45 percent who support it.
CNN's Kristi Keck and Brianna Keilar contributed to this report.