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If Sen. John Kerry (search) is elected, his presidency is likely to bring a sharp shift in White House direction — along with pragmatic backpedaling on some of his boldest campaign promises.

From his ambitious health-care proposal to his pledges to add 40,000 troops to the military and 10 million jobs to the economy, Kerry has a multitude of multi-pointed plans, and he talks optimistically about making them reality.

Corporate tax loopholes? Gone "in a nanosecond," says Kerry. The Bush administration's new overtime regulations? Reversed on day one, says running mate John Edwards.

And yet Kerry, a four-term senator, has been around Washington long enough to know how hard it is to get things done in an era of divided government, high budget deficits and war. Already, he has scaled back his child-care assistance and national service plans due to tight dollars and his pledge to follow a "pay-as-you-go" style of governing.

Kerry talks openly about the limitations he would face as president.

Asked recently what he would do to stop genocide in the Sudan (search), Kerry told a TV interviewer he'd do "everything possible," but he added that "our flexibility is less than it was" because of the demands from U.S. commitments in Iraq and Afghanistan.

Reflecting on the past few years, with Republicans running both houses of Congress, Kerry said: "People don't understand what it's been like to have a House of Representatives run by Tom DeLay, and Republicans in the Senate run by a group of ideologues, and it's been hard to deliver things to people — anything to anybody."

Even if Democrats make inroads on Election Day, the next Congress is sure to remain sharply divided and highly partisan.

Kerry's maneuvering room would be further limited by the War on Terror and the situation in Iraq, which are sure to dominate the attention of the next president. Usama bin Laden and other Al Qaeda leaders are at large, and Kerry's plan to "win the peace" in Iraq contains many question marks.

"His governing will be dictated by events that are imposed upon him, regardless of how he wants to govern, and the critical one will be Iraq," said Marc Landy, a political science professor at Boston College.

Landy's shorthand description of Kerry's approach to Iraq: "Bush without the swagger," following through on U.S. commitments while trying to get more support from other nations. But Landy said Kerry will be under intense pressure because many of his supporters simply want America to get out.

"Even John Kerry doesn't know what do about that, because it's such a nasty choice," Landy said.

Kerry's goal of beginning a drawdown of U.S. troops within six months and completing it in four years is dependent on the willingness of allies to shoulder more of the burden — anything but a sure thing. But he can sweeten his pitch for more international assistance by dangling a share of the reconstruction dollars that Bush has largely reserved for American companies.

Stylistically, the shift from Bush to Kerry would be dramatic. Where Bush is prone to short, simple declaratives and a Texan's folksy mannerisms, Kerry is a reserved New Englander known more for meandering deliberation and a self-described tendency toward "Senate-speak."

Still, former campaign manager Jim Jordan says the senator is sure of himself when making decisions on policy. "Although he is indisputably one who possesses progressive instincts, he's very rational and very, very practical. I think he would govern much like Clinton did," Jordan says.

Long a Senate backbencher without a leadership role, Kerry has little experience as a chief executive to evaluate in predicting his governing style. He appears to favor a fairly flat organizational structure, giving many aides access to him, rather than the more hierarchal organization associated with Bush.

"His leadership is based on extensive consultation," says Darrell West, a political scientist at Brown University. "He's not going to be an impulsive president."

Kerry's intimate knowledge of Congress and its key players could be helpful, West said, but there is also the risk that "familiarity breeds contempt."

"We know he's not a warm and cuddly guy," West said. "He may not have the personal relationships that are helpful."

Former Democratic Sen. Bob Kerrey (search), who served with Kerry, says that on both domestic and international issues, the presidential contender has shown "he's not naive when it comes to getting people to work together" on difficult problems.

Kerry's work in the Senate to normalize U.S. relations with Vietnam and resolve questions about American POWs there displayed "an open-mindedness that is going to be needed on problems from Iraq to Social Security, where people tend to draw an ideological line in the sand," Kerry said.

In areas where Kerry could act unilaterally, meanwhile, he could be expected to issue a staccato series of policy reversals, returning a wide range of regulations on the environment, abortion and other issues to their Clinton-era status. Kerry also would move quickly to lift Bush's executive order restricting medical research involving embryonic stem cells.

More broadly, Kerry's administration could be expected to bring a new approach across the horizon: tougher on polluters, less heavy-handed in using anti-terrorism statutes, more amenable to addressing global warming, hostile to even partial privatization of Social Security, opposed to drilling in the Arctic National Wildlife Refuge, to name a few.

The path is less clear on some of Kerry's signature campaign proposals.

Kerry says his first order of business as president would be to "send Congress a health care plan that stops spiraling costs, covers every child in America, and makes it possible for every American to get the same health care as any member of Congress."

But the sheer scope of the proposal and the price tag — anywhere from $653 billion to $1.25 trillion over 10 years, by outside estimates — guarantees plenty of resistance. He's made other big-ticket proposals as well: a $2,500-a-year tax credit for college tuition, for one.

Kerry says he can finance his proposals by rolling back Bush's tax cuts for the wealthiest Americans, closing various loopholes and getting allies to help share the burden in Iraq. But there is huge skepticism that he could deliver all he has promised and still meet his promises to cut the deficit at least in half within four years and not to raise taxes on people earning less than $200,000.

"On the big stuff, on Iraq, on the tax rollback, I don't see Congress being cooperative," said Barry Burden, a professor of government at Harvard University. Still there are other areas where Congress might be more amenable.

For example, Kerry's calls to increase financial support for schools under the No Child Left Behind (search) law and to strengthen homeland security by doing more to protect ports and inspect airline cargo would be hard for Congress to resist politically, Burden said.