After sitting at Gordon Brown's side in the Cabinet Room yesterday, John McCain went to the House of Commons, where a gaggle of onlookers shouted, "It's the next president of the United States!" as he was greeted by David Cameron and a line of honour of senior Tories, including William Hague, George Osborne and Liam Fox.
The 71-year-old Arizona senator joked with Mr Brown about his exhausting schedule during a whirlwind visit to Iraq and Europe. But he had a spring in his step as he emerged from 10 Downing Street and headed for the television cameras. For the folks back home, he wanted to be interviewed in front of that famous front door.
Not to be outdone, Mr Cameron's team organised an equally good backdrop for Mr McCain's photocall with the Tory leader. They won permission from the Commons authorities for the two men to be filmed in New Palace Yard, just under Big Ben.
The man who will be the Republican Party's standard-bearer in November's presidential election was certainly in demand on his brief visit to London. Mr Brown, who had not met Mr McCain before yesterday's 45-minute session, knows he may be installed in the White House by next January.
Privately, the Prime Minister's sympathies might lie with Hillary Clinton or Barack Obama but diplomatic niceties prevent him taking sides – either between America's two parties or even within them. When elections are in the offing on either side of the Atlantic, politicians of all hues take refuge in bland statements about how the close relationship between the two nations will continue.
Yesterday was no exception. "We expressed our great appreciation for the longstanding and unique relationship that exists between our two countries, our common values and our common efforts that are made by both countries on national security and others," Mr McCain said after his talks with Mr Brown.
Before his visit, the plain-speaking senator had expressed concern about conditions in the Basra area following the withdrawal of British troops from a "combat" to "overwatch" role. "With all due respect I remain concerned about the situation in Basra," he said a week ago. "There are different factions that have taken over certain areas. Everybody knows that, it's not a secret."
Yesterday, he preferred to pretend it was a secret, repeatedly refusing to be drawn on what he thought about Mr Brown's plans to bring home the remaining British troops in Basra.
He said it was a matter for the British Government how long the UK maintained troops there. "I fully appreciate that British public opinion has been frustrated by sometimes our lack of progress in both areas [Iraq and Afghanistan]. All I can do is express my gratitude to the British Government and people, especially the brave young people who are serving," he said.
Despite the apparent differences over Basra, Mr Brown and Mr McCain bonded over climate change. He would take a more proactive role than President George Bush, which would not be difficult. The Prime Minister was encouraged that Mr McCain had read his speeches about reforming international bodies. He gave a warm response to Mr Brown's plan to turn the World Bank into a World Environment Bank.
Mr McCain did not need to waste time on introductions with Mr Cameron. He spent time with him when he addressed the 2006 Tory conference and has hailed Mr Cameron as a "Tory JFK". Yesterday the two men discussed their common brand of "modern Conservativism" – and how they can broaden its appeal.
For a while, the Conservative Party was in the deep freeze at the White House after Michael Howard, Mr Cameron's predecessor, criticised some aspects of the Blair government's actions in Iraq. But the ice seems to have melted, as Mr Howard joined the talks with Mr McCain yesterday.
Mr McCain, who held a £500-a-head fundraising lunch at Spencer House, will meet Nicolas Sarkozy, the French President, in Paris today before returning to London for a sightseeing trip at the weekend.
Although Mr McCain was on confident form, he will not take for granted what the Westminster crowd shouted. After all, Al Gore now introduces himself as "the ex-future president of the United States".