First he ran away from his own party on campaign finance. Next he ran at the heart of the congressional ethos by taking on Big Pork. Then he ran against the anointed darling of the Republicans, Gov. George W. Bush.

Two years ago he ran against the conventional wisdom and captured the Republican presidential nomination. Now, in a brutal primary in the brutal heat of an Arizona summer, he is running against his own record.

No one ever said Sen. John McCain was an ordinary politician.

Reared in a family of admirals, McCain was a rebel. He joked his way through childhood, caroused through Episcopal High School (where, naturally, he was a wrestler) and was remembered more for his pranks than his work ethic at the Naval Academy (this time his sport was boxing). His record at Annapolis was so dismal that only five men graduated behind him. As a naval aviator, he nearly died twice, sat isolated in a Hanoi prison for years, and returned to America scarred but not scared. McCain entered the House a war hero in the early 1980s, became a raucous, moral force in Washington and soon moved on to the Senate.

The attack against McCain this summer comes from the right, where it often has come, with former Rep. J.D. Hayworth, tea leaves on his breath, mounting a Republican primary challenge against McCain, who may style himself a rebel but who believes devoutly in two of the sturdiest institutions in American life: the military and the Senate, where he is seeking a fifth term.

Sailing against the wind

But McCain is not a weathervane, which shows which way the wind blows. In the argot of an East Coast political family, the Kennedys, he is willing to sail against the wind. Instead, McCain is a barometer, which measures the pressure exerted by the political environment.

Indeed, the place where McCain is this summer — under high pressure from an outside force — shows precisely what’s happening in American politics at the moment and is precisely the place where his former Senate colleague and 2008 election rival, Barack Obama, finds himself as well.

McCain is an eager pugilist but a reluctant partisan. He teamed up with a liberal Democrat, Sen. Russ Feingold of Wisconsin, to fashion a campaign-finance overhaul that Republicans curse to this day. Democratic presidential nominee John F. Kerry wanted McCain as his running mate in 2004 — a move that would have scrambled the political calculus for a decade.

That, too, was Obama’s instinct. He wanted to change how Washington works and preached bipartisanship — which, more than anything besides his remarkable biography, was what separated him from Sen. Hillary Rodham Clinton two years ago.

The political din

If there was a temperamental difference between McCain and Obama, it was that Obama had distaste for what former British Prime Minister Harold Macmillan called “the heckling and din and having to attack and defend and all the rest of it.” McCain loved the heckling and the din and all the rest of it.

Now the two 2008 nominees find themselves in the same position — moving away from the middle and from their own bipartisan impulses. Maybe it had to be that way. Political forces in both parties are pushing away from the center and from each other.

McCain felt it first, and it may not be too much to say that the John McCain who ran in the 2008 general election was not the John McCain who ran in the 2008 primaries. Whether Sarah Palin was the cause or consequence of that change we may never know — but we know she was a consequential part of it.

By late 2009, the Tea Party was brewing a rebellion that even McCain could not ignore. Among the targets were Republican regulars, including McCain, who was unopposed in his last Senate nomination campaign and who won his fourth term with a breathtaking 77 percent of the vote against an opponent who spent only $12,716 — about what LeBron James will make for playing three minutes next season.

The pressures that have moved the McCain barometer have borne down on Obama too. The president didn’t want a stimulus or health care bill that had no Republican votes. No student of Social Security or Medicare, which had Republican support and have become unassailable components of the American economic landscape, would want that.

Friends to fall back on

It didn’t help that Obama had few Washington relationships to fall back on. The most successful Washington outsiders of the last generation, Ronald Reagan and Bill Clinton, were manic networkers who had spent years building relationships, Reagan as a four-time presidential candidate and two-term governor, Clinton as a five-term governor and onetime chairman of the National Governors Association.

McCain’s closest relationships are with pals Bob Dole of Kansas and Warren B. Rudman of New Hampshire, both out of politics, and Sen. Lindsey Graham of South Carolina, who has lost much of his enthusiasm for bipartisanship.

McCain swallowed his pride and invited former Gov. Palin to campaign for him this year, the political equivalent of what Winston Churchill, in extremis exactly 70 years ago in World War II, described as the New World stepping forth to rescue the Old. This is, after all, an environment where seven members of Congress who supported the 2008 bailout of troubled financial institutions known as the Troubled Asset Relief Program were defeated in primaries so far this year. Obama and McCain both voted for TARP.

“Picasso used to be a great painter,” the 20th-century French artist Georges Braque, one of the founders of Cubism, once said. “Now he is merely a genius.”

McCain and Obama are now merely geniuses. The two onetime presidential nominees, once bitter opponents, both confront a political landscape that is as different from the one they navigated in 2008 as a Rembrandt portrait is from one painted by Picasso.