Yesterday, Dean Baker and I argued that journalists should remember that they don't know what politicians think or believe, they only know what politicians say -- and their reporting should reflect that.

Now here's MSNBC's Kelly O'Donnell explaining Joe Lieberman's opposition to the Medicare buy-in a few minutes ago:

Some moderates, most notably Joe Lieberman of Connecticut, were against this idea, feeling it would put too great a burden on a federal program that's already stretched very thin.

No. Kelly O'Donnell does not know that Joe Lieberman feels any such thing. She knows he says it -- but, if she's been paying attention at all, she has good reason to suspect he isn't telling the truth.

See, O'Donnell didn't mention this, but Lieberman has supported the Medicare buy-in. He supported it as long ago as 2000, and he supported it as recently as three months ago. Between that and the fact that so many of his comments about health care this year have been false or inconsistent, there's no reason to assume his stated reasons for opposing the Medicare buy-in are true.

And, indeed, there is a growing universe of journalists who recognize this.

The NBC News political unit notes there is “growing evidence that Lieberman's objection to the Medicare 'buy-in' compromise isn't necessarily based on principle. ... This is why the charge of playing politics with the left is looking so believable to some.” The Atlantic's Marc Ambinder reports that “there have apparently been a number of private assurances given -- and broken -- by the Connecticut senator in recent weeks.” And even Lieberman defender Charles Lane says Lieberman is motivated by a desire for political “pay back.”

So why do Kelly O'Donnell and the New York Times continue to take Lieberman's claims at face value? Do they understand that when they do so, they're covering up -- rather than revealing -- what's really happening? That they're helping a politician mislead the public?