It's the nature of politics to question the authenticity of one's opponent. All politicians and their surrogates do it. The fact that it has become a common practice doesn't make it any less sleazy.

During the election season, politicians want desperately to be associated with "moments of grace" they can milk for partisan advantage. Blame it on total depravity and Republican strategist Lee Atwater, who taught a whole generation of pols to think and pray cynically.

If a politician's life can show evidence of a miracle or two, well, all the better to move the voters to think more kindly of the campaign on Election Day.

Republican presidential hopeful Sen. John McCain told an interesting story over the weekend about connecting with one of his North Vietnamese captors:

"It was Christmas Day," Mr. McCain told an audience at the Rev. Rick Warren's Saddleback Church during a forum that also included his opponent Sen. Barack Obama.

"We were allowed to stand outside of our cell for a few minutes, and those days we were not allowed to see or communicate with each other although we certainly did. And I was standing outside for my few minutes, outside the cell.

"He came walking up. He stood there for a minute and with his sandal on the dirt in the courtyard he drew a cross and stood there a minute later, he rubbed it out and walked away. For a minute there, [we were] just two Christians worshipping together."

This story also appears in John McCain's 1999 best seller "Faith of My Fathers," where he included this detail on Page 228: "I saw my good Samaritan often after the Christmas when we venerated the cross together. But he never said a word to me nor gave the slightest signal that he acknowledged my humanity."

It's an interesting story and a moving one -- if true. But as an armada of lefty bloggers have gleefully pointed out, the anecdote bears more than a supernatural resemblance to a story by Soviet-era dissident Alexander Solzhenitsyn about his encounter with a Christian guard in Stalin's gulags decades ago.

The story of how Solzhenitsyn's guard, obviously Russian Orthodox in his sympathies, drew a cross in the dirt has been in the air ever since the former dissident's death earlier this month unleashed a torrent of fascinating anecdotes and tributes about his life.

Because Vietnam is an overwhelmingly Buddhist country, the likelihood of John McCain "worshipping" with a secret Christian among the atheistic Viet Cong strikes many as being as big a miracle as the Virgin Birth the holiday is based upon.

But as one of my colleagues reminded me yesterday, the Catholic Church has had an enormous presence in Vietnam for decades. Just because it happened to Solzhenitsyn doesn't mean it didn't happen to Mr. McCain, too -- that's the miracle of religious dissent in the face of totalitarianism.

Fair enough, but as an anecdote in a highly charged political season, a cross-in-the-dirt story from a guy not known for his piety sounds opportunistic. Because the McCain campaign has been cynical about so many things, the candidate may not be getting the benefit of the doubt he may be entitled to.

Further complicating belief in Mr. McCain's story is the fact that this dramatic tale is missing from his lengthy first-person recap of his experience in the May 14, 1973, issue of U.S. News & World Report. Again, just because he has only seen fit to mention it decades later in the heat of a presidential race steeped in civic religiosity doesn't mean it didn't happen. Perhaps he didn't consider it important enough to recount at the time.

Still, we can imagine what the swift boaters currently bedeviling Barack Obama would have done had the Democratic nominee told a similar story under the circumstances.

Memory is an amazing thing. Last month, Mr. McCain told KDKA-TV that he recited the names of the Steelers' defensive line to his Vietnamese captors. In his book, he recalled giving the Viet Cong the names of the offensive line of the Green Bay Packers.

Was he pandering to an important constituency in Western Pennsylvania -- or merely suffering an embarrassing memory lapse? (His campaign later said that the senator simply made a mistake by naming the Steelers this time.)

Between now and Election Day, every word uttered by the presidential hopefuls will be scrutinized for evidence of political and moral turpitude. There isn't a whole lot of interest in giving the "other side" the benefit of the doubt. When it comes to picking our next "Christian president," there's more than enough doubt to go around.