There are signs of what could be a shift in the news media conventional wisdom: for the first time in months, some key pundits are hinting and even saying that Senator Barack Obama could lose the Democratic nomination to what has long been described as a seemingly-impossibly behind Senator Hillary Clinton.

These kinds of cracks in the conventional wisdom often signal the beginning of a major shift, totally negating what earlier conventional wisdom steadfastly suggested “had” to be true.

The catalyst: Clinton’s win over Obama in Pennsylvania. Even though it was expected, the recent bad publicity surrounding Obama on several fronts, his campaign being on the defensive, the unrelenting push by Clinton on several fronts, and the realities of how American politics works in the 21st century have started to change some media thinking.

Newsweek’s Eleanor Clift is exceedingly blunt:

I’m beginning to think Hillary Clinton might pull this off and wrestle the nomination away from Barack Obama. If she does, a lot of folks—including a huge chunk of the media—will join Bill Richardson (a.k.a. Judas) in the Deep Freeze. If the Clintons get back into the White House, it will be retribution time, like the Corleone family consolidating power in “The Godfather,” where the watchword is, “It’s business, not personal.”

Not that anyone will be sleeping with the fishes with Hillary in the White House, but with the Clintons it’s business and it’s personal. Just think of all the scores to settle, the grievances to indulge.

Clift details how the Clintons were often at odds with Washington officialdom, which never liked them anyway. She notes how now some conservatives are cheering for her…and not only because they think they can defeat her. She is winning some fans due to her all-encompassing push to win no matter what. She writes:

Now the burden is on Obama to win the next round of primaries on May 6. He has said publicly that Indiana could be the tiebreaker, a prediction he could come to regret. If Clinton can win Indiana, hold Obama to single digits in North Carolina, and then run up a big margin in Kentucky on May 20, where she’s leading in the polls, she could overtake Obama in the popular vote. “We have to win big and lose small,” says an aide. Obama may yet discover his inner Rocky and recast himself now that the media is turning on him. It’s hard to be the next new thing for 15 months, which is how long he’s been running. And it’s time enough for Hillary to win ugly, if that’s what winning takes.

The New York Times’ Bob Herbert is more subtle but he hints at the same inkling of an idea:

Barack Obama is winning, so why does it look like Hillary Clinton is having all the fun?

Senator Obama has been thrown completely off his game by a combination of political attacks (some fair, some foul), a toxic eruption (the volcanic Jeremiah Wright was a gift from the gods to the Clintons and the G.O.P.), and some pretty serious self-inflicted wounds.

You can almost feel the air seeping out of the Obama phenomenon. The candidate and his aides are brainstorming ways to counter the Clinton death-ray machine and regain the momentum. They need to generate some new excitement and enthusiasm, and they need to do it soon.

Despite all the new voters who have been brought into the process, Democrats are filled with anxiety about their prospects in November. A nervous operative told me on Friday: “If we lose this election, it would be like Johnson losing to Goldwater.”

Herbert notes that part of what’s going on is the polarizing nature of the campaign, anger among Democrats but there is a constant:

Their message varies, depending on whether it’s in public or behind the scenes. But the mantra is roughly as follows: Obama won’t win! He can’t win whites. Jeremiah Wright! He can’t win women. He can’t win Hispanics. He’ll lose Jewish voters. Farrakhan! We’ll nuke Iran.

The share of Clinton voters who have been telling exit pollsters that they will not vote for Senator Obama if he wins the nomination is inching toward the red zone. At the same time, there is growing resentment of the Clintons’ tactics among Obama partisans, especially the young and African-Americans.

While he doesn’t say Clinton could well win, the hint is there:

Hillary Clinton may be behind, and she may lose. But she is now widely seen as the tougher of the two candidates, the one who is more resolute, who will fight harder and longer (and, yes, more unscrupulously) to achieve her desired ends.

An edge in toughness is hardly a good quality to cede to your opponent.

….Some Democratic officials who were worried about having Senator Clinton at the top of the ticket in November are now expressing concern about Mr. Obama. Mrs. Clinton’s bar-brawl tactics have raised her negatives sharply, but they’ve also raised doubts about Mr. Obama. Is he a fighter? Is he tough enough to take on the G.O.P.?

One of Senator Obama’s favorite phrases is “the fierce urgency of now.” There is nothing more fiercely urgent for him right now than to reassure voters and superdelegates that an Obama candidacy will not lead to a Democratic debacle in November.

Some Democrats and Obama supporters in general are likely to dismiss Clift’s and Herbert’s columns as them taking the Clinton and/or Republican themes hook, line and sinker. That’s the modus operandi for partisans on both sides: question the motives of those who dare criticize your candidate.

But that’s clearly NOT what is happening here.

What’s happening is that Obama has long said he wants to change the political culture, a goal that many independent voters as well as many Democrats and Republicans would find highly laudable. But you can’t hope to change the political culture unless you’re in a position to change the political culture.

It’s sort of a Catch 22. Obama is going to have to show — and show soon — that his campaign in ideas, tactics, and energy can function in America’s polity — the polity as is. Not the polity as he and others might wish it to be. That means being more nimble, making the case for his candidacy, countering any Clinton charges, effectively answering lingering reservations that constituencies he is having problems with may have about him.

The bottom line reality that he’s facing is that just as Hillary Clinton is not entitled to the Presidency because she’s a Senator and a former first lady, Obama is not entitled to the nomination because his message is hope and change. Even when you do an job interview you have to aggressively overcome lingering objections.

Obama has to do that — and quickly. Because these two writers are now writing sentiment that is lingering “out there” and may increasingly be out there. If it goes “out there” enough so Superdelegates are concerned at a time when Obama doesn’t perform as well as he hopes in upcoming primaries we’ll see what we have seen so much when Campaign 2008 began last year:

The conventional wisdom will be revealed to be not so much conventional wisdom as to have been flavor of the day wisdom — a flavor that could change totally a day later.

And that would be delicious for Hillary Clinton.