I saw another man dance with Joe Biden's wife, Jill. It was almost three years ago, on the terrace of the sublime Villa d'Este on the shore of Italy's stunning Lake Como, and Mr. Biden watched, smiling broadly and sometimes laughing, as the man gracefully moved Jill around the dance floor. It was late, and the guests still there looked on keenly because Jill Biden's dancing partner was very good-looking and very famous. He was John McCain.

I tell this story to suggest that if anyone – including, of course, Barack Obama – thinks that Joseph Robinette Biden Jr. is going to play the usual role given to a vice presidential candidate, hatchet man, then the wrong man has been chosen. Mr. Biden is capable of the occasional gaffe, the sentence without end, the piquant but (literally) politically incorrect statement such as the one he made during the primary campaign – Mr. Obama is "not yet ready" to be president – but he has the essential decency that once was commonplace in Washington and now, alas, is taken for weakness and lack of proper fervor. Joe Biden is a gentleman.

In choosing Mr. Biden, Mr. Obama reached into the very heart of the Washington establishment – especially its foreign policy wing. In his many years on the Senate Foreign Relations Committee, both as a member and as chairman, Mr. Biden has come to know just about all the players. He has been at it so long – elected senator at the ridiculous age of 29 – that then-Capt. John McCain (U.S. Navy) was his military aide on some foreign trips. I applaud the choice of Mr. Biden, but the one thing he does not represent is change.

In fact, Mr. Biden represents the foreign policy consensus that Mr. Obama, and especially his followers, opposed – and in the latter case, abhorred. Mr. Biden voted for the Iraq War. He based his position on the received wisdom of that time – Saddam Hussein had weapons of mass destruction and needed to be taken out. Mr. Biden later recanted, said he made a mistake. But his mistake, he had to add, was predicated on the assumption that President Bush would not rush to war. That was his second mistake.

Yet if Mr. Biden was wrong on Iraq, he has been right on so much else – including that military force had to be used in the former Yugoslavia to end ethnic cleansing. He has been right, too, about the dangers of nuclear proliferation – a dull topic of merely life-or-death importance. Over the years, he has been loyal – to his party and to his president, even when that president was as irresponsible as Bill Clinton.

For Mr. Obama, the risk in choosing Mr. Biden is that he will, sooner or later, throw this highly disciplined campaign off-message. Mr. Biden has substituted loquaciousness for the conventional and more colorful weaknesses of politicians. To quote something I once wrote, his mouth is his Achilles' heel.

In response to that column, Mr. Biden called and left a message. He thanked me for the column ... he needed to be told the truth ... it was good for him ... hard to hear, but in the end the sort of thing he needed to know ... of course, he had his reasons for going on so long – this was during the confirmation hearing for Supreme Court Justice Samuel Alito – since he had things to say ... points to make ... but yes, I was right, and he went on too long and he had to do something about that and it was good of me to point it out. Beep! The machine cut him off.

Gotta love someone like that.

Richard Cohen is a Washington Post columnist. His e-mail address is cohenr@washpost.com.