Three visions of a new White House

TUESDAY is D-Day for the ever more brutal primary battle between Hillary Clinton and Barack Obama as the last major state, Pennsylvania, goes to the polls.

A big win for Clinton will give her the hope of salvaging a campaign in which she has been browbeaten by the phenomenal support of her younger rival. Anything less is likely to confirm Obama as the nominee Democrats pick to face Republican John McCain in the November election.

But while the result lies in the balance, months of campaigning have given a clearer view of how the world might change with a Clinton, Obama or McCain White House.

Here, Scotland on Sunday looks at how each of the three could win the presidency and what they would do once installed in the Oval Office.

How Obama would become the next US president

Barack Obama has already announced what may amount to the 'end game' of his campaign, declaring himself in favour of ending his marathon of TV debates with Clinton.

It comes with a recognition among his staff that, if he can avoid verbal gaffes, such as a speech when he labelled small-town Americans "bitter", he is coasting to victory.

Polls say he will lose by single figures to Clinton in Pennsylvania on Tuesday but make up the ground with victories in Indiana and North Carolina on May 6.

His task from now on is simply to avoid making statements that dent his national polling lead of around 9%.

With Clinton unable to catch his lead of between 130 and 160 delegates, his path to victory would lie in the 350 uncommitted party-appointed superdelegates, including heavyweights Jimmy Carter, Al Gore and Ted Kennedy, conferring in June, as suggested by Senate majority leader Harry Reid, to anoint a winner.

By then Obama will have 1,900 primary delegates. Another 150 plus of the uncommitted 'supers' will take him past the 2,025 he needs for the nomination.

Many of these votes could come from Clinton supporters who conclude that it would be political suicide for the party top-brass to nominate Clinton if the voters have gone for Obama.

The nomination itself will not come until the August convention, but under this scenario, Clinton, sensing humiliation if she stays in the race, will bow out.

What he would do…

Obama would then see a surge in support with rock festival-style summer rallies, beating McCain in November by hammering him on the twin ills of a deteriorating economy and the Iraq war.

Obama has offered a new engagement with the United Nations and with allies, leading some to hope for a rebirth of the Special Relationship that will relieve Britain of its high-wire act of choosing between pleasing Washington and pleasing Europe.

Obama has drawn praise and criticism in equal measure by declaring he is willing to talk to world leaders, even those of America's adversaries Cuba and Iran, in order to promote peace. His supporters say this will ease global anti-American sentiment kindled by the invasion of Iraq – a war Obama opposed. Others say such meetings risk handing propaganda triumphs to the world's tyrants.

There are expectations of a new commitment to human rights, including hopes that under Obama the US will join the International Criminal Court.

But Obama's new engagement with the world will also contrast with a more protectionist trade policy. He has promised to give tax breaks to US manufacturers and renegotiate the North American Free Trade treaty, leading to fears of new trade barriers.

How Clinton would make it to the Oval Office

Hillary Clinton's path to success in this primary election depends on her reported ace in the deck – strong support among party officials.

These party officials, who comprise the superdelegates, will be nervous of making her the nominee if Obama wins the popular vote. But if she can even the score of elected delegates, they might change their minds.

To this end she will hope for Obama to make some gaffe, or be hit by a personal revelation that sees voters flock to his rival.

Alternatively, she could hope to reinstate the delegates of the Florida and Michigan primaries, who are suspended after both states moved forward the dates of their primaries without permission.

If Clinton can get a majority on the Credentials Committee at the Denver Convention, that committee could reinstate these delegations, allowing Clinton to close the voter gap.

It looks to be a tall order. Obama was not a candidate in Michigan, and would argue that reinstating their delegates is wrong and possibly illegal.

A bumpier strategy would be for Clinton to demand the nomination as the price for ending an ever more damaging race. Many party top brass fear that if this battle drags on into summer, the Republicans will benefit.

One possibility suggested by Clinton and husband Bill is for Obama to agree to be her vice-president, although he has ruled out such a move.

If Clinton gets the nomination, the path to victory against McCain would follow similar lines to Obama's, hammering McCain on the twin failures of the Bush administration, the war and the economy.

What she would do…

From the outside, a Clinton White House might look much like an Obama one. Both senators have promised new engagement with the world, even as they call for an end to free trade that has seen millions of American jobs exported, principally to China.

Clinton's foreign policy approach appears more cautious than Obama's, and she has castigated him for offering to talk too readily with America's enemies. "We have a choice in who we associate with," she remarked in last week's presidential debate.

Like Obama, Clinton has promised to end the Bush administration's virtual blackout of the United Nations. Clinton can also draw on experienced foreign policy officials, many of whom served in the presidency of her husband, Bill.

Like Obama, she promises early withdrawal from Iraq, a move that would allow Britain to pull out troops it badly needs to deploy elsewhere.

But, as with Obama, Clinton's new international engagement comes with a caveat for Britain: Gordon Brown will have to compete for favours with France, Germany, India and Japan, all eager to be seen as the partner of a new, more open, US administration.

How McCain would defeat the Democrats for the top job

McCain's strong suit in the presidential race is the potentially self-destructive battle between Clinton and Obama. The nastier their spat becomes, the more the crucial swing-voters may decide he is the man best trusted with the nuclear briefcase.

And even after the Democrat battle is over, if his presidential rival is Clinton, he will remind voters of her false claims to have braved sniper fire in Bosnia and cemented peace in Northern Ireland during that contest. He will also highlight the millions of dollars her husband has garnered from foreign benefactors, suggesting that these donors will expect big favours once she is in office.

Against Obama, McCain will highlight his association with controversial black pastor Jeremiah Wright, and his apparently condescending characterisation of "bitter" small-town Americans.

And though he has been commendable in opposing such sentiment, he may draw support from millions of voters who do not want to see either an African American or a woman as president.

On the positive side, McCain will win support for his disarming charm, and his status as a genuine war hero, having suffered years of torture as a prisoner of North Vietnam. But perhaps his biggest advantage will be that he was not a member of the Bush administration. While supporting many of its policies, notably the invasion of Iraq, McCain can portray himself as standing for the ideals of Republicans, but not those of the Bush administration.

Finally, McCain's record of working with Democrats, notably fellow senator Joe Lieberman, is in line with popular sentiment which seeks a consensus candidate to end partisan divisions.

What he would do…

Like his Democratic Party adversaries, McCain has promised a new outreach to friends and allies in the world. Yet it is unclear how big a break he will make from Bush, with his advisers split between multilateralists and the Neo Cons.

The Republican senator has appeared to retreat on promises to close Guantanamo Bay, and it is unclear how much he would trust the United Nations to solve the world's problems.

Among commitments that have alarmed Western allies, he has declared that if he were president, he would boycott the opening ceremony of the Beijing Olympics in protest at violence in Tibet. And the senator wants Russia kicked out of the G8 group of industrial nations, accusing Moscow of a lack of cooperation.

Meanwhile, McCain's call for US troops to stay in Iraq for "100 years" will send shudders down the spine of Whitehall, which knows that this war remains a stumbling block to better relations with Europe.