"So Nixon was President in 1968, was he?" How the Hell did he get by with that for 20 years without anyone questioning it? Liberal media, that's how." ... "This guy won't carry ten states, no matter what the polls say now." 
Social Darwinism.
The "left" is unfamiliar with the entire concept of social Darwinism. They don't know it. They can't apply it.
In contrast, the "right" is under such constant media assault that we've culled our own herd. The left has made us stronger by attacking us from every angle. Our weaker candidates are killed off early on, and only our strongest have survived.
The biased news media hurts us in the short term, of course (I'd guess 10 to 15% in the polls), but over the long term it has made us stronger. Vas mich nicht umbrincht, mass mich starker, and all of that. Our weaker politicians like Newt Gingrinch, who had far more vulnerabilities than strengths, are drummed out. Our Packwoods are gone. Our Lott's are no longer in charge of the Senate (for giving a compliment at a freakin' birthday party!).
What remains in our Party are the strongest. President Bush and VP Cheney are so strong that the left has to now manufacture from whole cloth entire "scandals" such as NY Times' columnist Maureen Dowd deliberately misquoting the President in order to smear him.
Quote Senator Kerry verbatim on his "I voted for the $87 Billion before I voted against it," however, and we get tagged as being "mean-spirited," "negative," etc.
So the same process that makes our side stronger (we've now taken the House, the Senate, the Presidency, most state governorships including all of the large states, most state legislatures, etc.) makes our opponent weaker.
Because the news media protects instead of culls its own liberal herd, that herd has grown progressively (heh, or regressively if you must) weaker. An Arkansas governor with a long track record of failing his own state's schools, womanizing, and questionable (that's being charitable) business deals gets such sweet press that he wins the Presidency, only to be so out of his league in the White House that he fails to enact any of his ideological legislation, for instance. A corrupt California governor is so protected by his liberal news media that citizens have to recall him to stop his statewide fiscal disaster, instead of being compelled to resign by non-stop news attacks. The LA Times put 27 more reporters covering allege "groping" claims from unemployed actresses against Davis' Republican challenger than they sent to uncover Bustamante's questionable La Raza affiliations, or on various scandals involving state "grants" to liberal "charities," much less to cover such news as the bribes taken by a French President that could explain his ardent opposition to a war on Iraq.
A Democrat can sexually harass a staffer in New Jersey and be called "noble" for admitting that he's gay instead of a cad for hitting on his staff, betraying his wife, or even called a crook for misusing state funds to entice new lovers. But let a Republican Senator kiss a staffer on the lips, or a conservative Supreme Court nominee give a staffer a can of Coke, and suddenly they are misogynistic sexual harassers in the eyes of the news media.
Can you imagine the news media's collective reaction if a Republican had instead made Senator Kerry's comments about Britain, Italy, Japan, Spain, and Poland being a "coalition of the bribed"?!
It is beyond question that there is a double standard in the media. In the short term, this double standard does indeed work against us by giving several percentage points of popular support over to the Democrats.
In the long term, however, Social Darwinism kicks in. Our leaders are stronger, have better political armor, and maintain more easily defensible political positions. Our weaker politicians are gone. Their weaker politicians, however, are cultivated.
This is epitomized in their selection of Senator Kerry, the most liberal voter in the entire Senate, whose most significant acts of his life were made in the four months that he served in his first job out of college some 3+ decades ago...a man who has taken either both sides of every issue or the most liberal side of every issue, bar none.
Senator Kerry can get away, at least in the press of course, with voting for the Iraq War but then against its funding, but can you imagine what the press would have done if President Bush had been for our National Missile Defense but against its funding?!
So at every turn, the Left gets a free pass for its waffling inconsistency, whereas the Right has to get it correct the first time and stick with that view no matter what.
But Social Darwinism has caused unintended consequences. By coddling the Left via forgiving most every gaffe, the press has cultivated a weaker liberal side. And by attacking the Right from every possible angle at all possible times, the liberal press has made the Right stronger.
It's Social Darwinism. The herd that has been more pampered has grown soft. The herd that has had to fight has grown stronger.
The left is now stuck with mediocre candidates. The right, however, is finally raising up a crop of Titans.
5 Legislative Days Left Until The AWB Expires
I think too much is made of this "Anybody but Bush" stuff. What Kerry really represents is "Anybody but Dean."