Sen. Barack Obama lost Nevada after failing to fully respond to a myriad of baseless attacks from the Clinton campaign.

In South Carolina, he faced them down loudly and directly. And won the first blowout of the presidential race.

He may not have gotten back on offense as much as he could have.

But he was able to stick to his main campaign message about changing the political system while counterpunching. He played defense without getting knocked off stride and back on the heels.

Credit must also be given to Obama's organization, which rejected the old Carolina establishment politics of winning support through "walking around money," in favor of building a grassroots team from the bottom-up.

A general election campaign is going to need both qualities: energy from the grassroots, led by a candidate who can effectively respond to and triumph over nasty attacks.

After Nevada, Obama quickly learned the lesson he needed to learn.

Thank the Clintons for putting him through his paces. If Obama is to be the nominee, he needed to be battle-tested. Now he is, and a better candidate for it.

But don't thank the Clintons for much else. If Obama learned a good lesson this week, the Clintons learned nothing.

After seeing their attacks backfire in South Carolina, and despite all the times in recent months and years when stoking racial divisions has backfired, they are again ramping up the too-clever-by-half race-baiting.

Bill Clinton said yesterday that Obama's win is no different than the primary victories in the 1980s of Rev. Jesse Jackson -- clearly seeking to blunt Obama's momentum by equating him with a black political figure less respected by many white Americans.

And, as Talking Points Memo flags, unnamed Clinton campaign officials told the Associated Press that "they believe the fallout [from the past week of attacks] has had the effect of branding Obama as 'the black candidate,' a tag that could hurt him outside the South."

LiberalOasis has long avoided making endorsements in intra-party contests.

Unity and coordination are necessary to defeat the conservative machine, often requiring liberals to put aside secondary differences and focus on common ground.

And if Clinton becomes the nominee, that unity will be required again.

Her stated policy positions (universal health care, cap greenhouse gas emissions, no permanent bases in Iraq, etc.) are good enough to shelve any concerns and fight on together.

But the divisive way she is running her campaign is anathema to the core liberal principle of a government representative of all, a principle that is the foundation of the Democratic Party.

After the last several decades, no one is naive enough to believe that you can win a national campaign without getting tough.

But you can get tough on issues, using facts.

If you believe stoking racial divisions is the only way to win, there's another political party you can join.

A candidate that cannot live up to his or her party's principles is a candidate that undermines trust in that party.

In turn, the Democratic Party is better off without the Clintons leading it.