I don't know why you think that the WaPost is such a liberal paper. Compared to trash like Fox News and Washington Times I guess, but compared to most large news outlets they have a very unbiased newsroom.
I don't know bro, the Post endorsed President Obama... twice... and when a newspaper's own ombudsman says things like this, that's a pretty good indicator of a liberal tilt:
...some of the conservatives' complaints about a liberal tilt are valid. Journalism naturally draws liberals; we like to change the world. I'll bet that most Post journalists voted for Obama. I did. There are centrists at The Post as well. But the conservatives I know here feel so outnumbered that they don't even want to be quoted by name in a memo.