Why doesn't a tough reporter just cowboy up, challenge Bush's BS, & call him a liar?

Here’s a link to a Washington Post article about Scott McClellan.
The piece itself discusses how little McClellan has to say at times. Of course, “sacrificial lamb” is probably somewhere on his resume - you can’t talk to the President like this, but the Press Secretary is another story. It does include this exchange:

Well, you have to admit there’s a percieved attitude difference between “Mr. President, on this date you said X, but this source from your own government says Y. What comment do you have?” and “Bush, you are a goddamned liar” (which is what the OP seemed to be advocating).

The closest I can recall to something like that was in Reagan’s 1987(?) Iran Contra press conference. Sam Donaldson asked some pointed question and Reagan came back with what seemed to me a canned replay and Donaldson snapped back something like (very agressively) “Mr President, the American people simply don’t believe you!”

As for McClellan save your sympathy. The back and forth during the daily press briefings is much higher and less deferential. It’s his JOB to take bullets for the President. Hell, McClellan’s been beaten up, it’s true, but it’s been NOTHING like what happened to Mike McCurry during the Monica Lewinsky thing.

McClellan gets questions about the President commenting on ongoing investigations and ‘did the President lie about WMD in Iraq’. Well and good.

McCurry got ‘Mike, is the semen on that dress the Presidents?’

Christ, if there’s a low point in a press man’s career it’s that question. Ugh.

AFAICT, the people most “damaged” by Joe McCarthy were anticommunists themselves and Republicans. This was because his self-serving, partisan grandstanding about Communist infiltration in government (most of which had been detected and eliminated by liberal bureaucrats in the 1940’s) didn’t actually accomplish much except to discredit anticommunist concerns as “witch hunting”.

From a panel discussion on Coulter’s book Treason:

I can confirm that, as far as the KGB files go, while there was heavy infiltration earlier, reaching all the way to the White House at one point… (a nephew of Roosevelt, IIRC), by the 50s, it was all but gone. Source: The Sword and Shield, the Secret Files of the KGB.

Oh, he gets no sympathy from me. He’s a boring, obfuscating motherfucker. But as you say, that’s pretty much the name of the game for the press secretary.