"On the March" is too strong.  And, as you point out, this latest round of elections says nothing about the relative strengths of the parties.  But, I think it is critical that Democrats do not get complacent right now.  This is our time to work hard and to bring the change we want in our country.  The Republicans are literally in the mirror and closing fast.  They are not going to remain in their current position for long.  They will learn how to use the internet to organize.  They will come up with a fresh round of irrelevant selling points (death tax, anyone?) and they will work very hard to turn the economic downturn into Obama's recession.

I also think it's natural to believe that the Democratic party infrastructure has undergone some radical transcedent changes from a few years ago.  But to me it seems that we have a similar infrastructure to what we had before with a major boost from Obama's celebrity power and a small boost from Dean's 50-state strategy.  This is not to denigrate the campaign Obama put together, but I think it's important to realize that the current Democratic ascendancy is the result of an improbable confluence of events rather than by sheer overwhelming organizing or messaging force by the Democrats.  We will need to work extremely hard to maintain the position we now enjoy.

A national party no more as someone from the region said...

"I submit, however, that this is reading way to much into these elections. First and foremost, the Republicans' problem isn't that they can't win in the south -- it's the exact opposite, in fact. Republicans are facing so much difficulty nation-wide because their focus is so overwhelmingly on the South."

Couldn't have been stated more clearer!!  In fact it is so... obvious now.  Looking back at Obama's path to victory, other than Missouri (which blew it's opportunity to keep one of the most impressive streaks of picking the winner of the election)the rest of the states that voted for McCain are truly the BASE of the GOP.  Remarkably, the U.S and a GREAT MAJORITY of our states has FINALLY woken up to the fact that Democratic Governing is the best way out of this MADNESS!!!  

and that these wins in the deep south don't mean that the GOP is not a regionally confined and out of touch political party, then more power to them.

That LA-04 and the Georgia Senate race even went to a runoff. The R candidates should have been easily over 50 percent there on November 4.

LA-02 is a special case. I would bet a lot of money that the Republicans will not hold that seat.

The Republican "dominance" of the south really translates to a small sub-area of North Texas, LA, and OK plus the northern third of Georgia (newer Atlanta suburbs).  

The rest of the south is pretty even or a small Democratic edge.  

Look at the maps of the House and the results are scary from a Republican perspective.  Non-coastal California.  North Texas, OK and LA.  The farm states.  50/50 in the rest of ths south.  After that?  Desperation.  The gerrymanders in OH,IL,MI, and PA have been overwhelmed by voting changes.  New England's been lost.  New York went from 18-13 D in 1992 (similar totals to today, nationally) to 26-3 D as of January.

Cilizza is trying to compare apples and oranges.

The 2004 House special election wins were signs that Democrats were reconsolidating at the grassroots all over the country.  The last white conservatives left the national Party in 2001/02 and we had dealt with it.  Democrats went on an amazing run in special elections at the state legislature level starting in iirc 2005 and lasting through this year in all but the most Red states.

We lost the 2004 election, sure, but Republicans pretty much only gained House seats due to regerrymandering in their favor in Texas.  The Senate seats they gained (and which contained most of the mandate of that election) were almost all in the South iirc.  The votes they gained that election were due to activating white voters in their fifties and sixties all over and previously nonvoting moderate and conservative white churchgoers mostly in the South.  In effect the 2004 election made them an even more Southern white party than before: their big margins and wins were there.

The 2006 and 2008 elections, and the slow dying out of the socially conservative, 80%+ white Greatest Generation cost them Northern moderates and their last true demographic grip in big chunks of Blue Statia.

What we are seeing now is Republicans consolidating themselves in the South (or, more exactly, all the Confederate heartlands.  Brigham Young would have joined the Rebellion if Lincoln hadn't surrounded Utah Territory with cavalry.)  They are knocking off conservative Democrats, aka Old Democrats.

And that is rather predictable.  The Old Democrat power in the South seems to me predicated on (a) more reliably heading off racial violence and (b) more socioeconomically equitable overall distribution of tax dollars.  That assumes conservative Democrats or attitudinally pre2005 Republicans in control of DoJ and Congress, of course.

Now we have an Obama Administration controlling DoJ and a moderate to somewhat liberal Congress that cares about poor Southerners.  And the newer Southern Republicans (the generation that includes Crist, Jindal, Sanford, even Barbour) further down the food chain who can affect bad local racially loaded situations just aren't permissive of the old 'Teach Em A Lesson' racial violence anymore.

I didn't think Southerners would be as quick to vote out Old Democrats as they have been this year.  But Republicans run the Tennessee and Oklahoma state legislatures now, Louisiana escaped full Republican takeover in 2007 and doesn't seem terribly resistant to it now.  Democrats don't look ascendent in Mississippi or Alabama at the state level.  I don't know how well an all Democratic federal government in Washington helps Arkansas Democrats, who seem to have peaked.  Though it seems Democrats have passed their low marks, reformed somewhat and become more liberal, and are slowly making up some ground in South Carolina, Georgia, and Florida.