President Obama kicks off an eight-day European visit - and steps into a morass of economic conflict and sensitive political maneuvers - when he lands in London on Tuesday evening.

    Obama, who will arrive at Stansted Airport in Essex and take a helicopter to the Regent's Park residence of the U.S. ambassador, will start the G-20 summit at a Wednesday morning meeting with British Prime Minister Gordon Brown, the host who tried to push his "global new deal" economic stimulus plan to a joint meeting of Congress earlier this month.

    And the importance of the G-20? Robert Hunter, NATO ambassador in the Clinton administration, calls it "the big enchilada." John Bolton, U.N. ambassador in the Bush administration, calls it a "nothing burger."

    In speaking with The Hill, neither of the ambassadors, though, discounted the importance of Obama's trip as whole. While Hunter placed weight on the G-20 summit and said the following NATO meetings in France and Germany on Friday and Saturday would involve Afghanistan issues that might not play very well on Capitol Hill, Bolton said the importance of the NATO meetings would usurp the style-without-substance of the G-20 meet-and-greets.

    "Anytime you get that number of disparate countries together it's very hard to find common ground," Bolton said. "They will all push very hard to seem like there's unity of purpose."

    "There's only one meeting that matters and that's the G-20," Hunter said. "... That's the one the people of every country care about. In comparison to other meetings the important thing is to burn up the wires to get something that will be seen psychologically as reassuring to the financial markets and to the average Joe in each and every country."

    While Obama last visited Europe with a rock-star welcome, host Brown goes into the much-hyped meeting of the world's top 20 economies on much shakier ground. His political capital was savaged even more by a viral video last week of Daniel Hannan, a Conservative member of the European Parliament, blasting Brown as the "devalued prime minister of a devalued government" as Brown is seen smirking in the clip. The video, which has racked up more than 1.8 million views in seven days, came up third Tuesday in Google search rankings when Gordon Brown's name was queried.

    Does this make Brown's "global new deal" dead on its G-20 arrival? "It was never going to go anywhere," Bolton predicted, adding that Brown will likely push global cooperation on an issue such as aid to developing countries.

    Hunter said Obama would likely push for a global economic stimulus plan of some sort "only if he's already got his ducks lined up" - adding that he probably doesn't.

    Obama will also be faced with German Chancellor Angela Merkel, who, along with French President Nicolas Sarkozy, put her foot down last week and rejected calls from the U.S. and Japan for more stimulus spending.

    "There's only going to be one leader at that meeting and that's Obama," Hunter said. "I think [Merkel will] pull back. She has to do enough of whatever she feels she needs to do because she has a very tough election coming up in September. She will do enough to be able to go home and claim some credit."

    Bolton said Merkel and Obama will play nice for the cameras while they try to hide stark disagreements over more massive stimulus spending.

    "This is a case, rare as it may be, where I agree with the Europeans," Bolton said.

    Later on Wednesday, Obama was scheduled to have talks with Conservative Party leader David Cameron. The two met in July when Obama was on his European campaign swing, and Obama reportedly called Cameron a "lightweight" afterward.

    In the afternoon, the Obamas will have a private audience with Queen Elizabeth II, and in the evening all of the world leaders in attendance will be feted by the queen and Prince Phillip at Buckingham Palace.

    On Thursday, in addition to the G-20 meeting schedule, Obama is set to hold bilateral talks with Russia, China, Saudi Arabia, India and South Korea.

    "The first time, you have meetings like this with leaders of countries just to establish a personal relationship," Bolton said. "It would be a mistake to expect much substantive outcome."

    China, Bolton said, "may talk about the amount of U.S. debt they're going to purchase," while discussions with Russia could cover "issues not resolved by hitting the reset button."

    Hunter said the Russia meeting would serve to advance the partnership on common-ground issues, and the China meeting would build upon the visit by Secretary of State Hillary Rodham Clinton and "recognize that China is a bigger player across the board than it was in the past."

    After the G-20, Obama will head to the NATO meetings, where the focus will shift from the economy to shoring up support for his force-expansion plans in Afghanistan. This, Hunter said, will likely put a spotlight on the burden the U.S. is undertaking in an "open-ended" conflict that now includes aid to Pakistan, and could spark reaction on Capitol Hill.

    "To sell Afghanistan virtually anywhere in Europe is extremely difficult," Hunter said.

    After the NATO meetings, Obama heads to Prague to meet with European Union leaders. The outgoing Czech prime minister, Mirek Topolanek - his country holds the EU presidency - said last week that the U.S. stimulus efforts were the "road to hell."

    Obama will round out his trip on Monday and Tuesday with his first visit to a Muslim nation, the secular republic of Turkey. Obama had vowed to visit a Muslim nation within his first 100 days.

    Hunter said he believes the whole trip - and particularly the G-20 - will show the world how much they need Obama to succeed "because he's the only one doing anything sensible and forward-leading."

    "The secret ingredient is the president's immense popularity, charisma, and the fact that he's proven himself to be a leader," Hunter said.

    Bolton, who stressed that Obama's real political test will come at the NATO summit, said the European trip "will show the limits of his personal popularity."