Check out this hilariously convoluted argument on Power Line for why the GOP had a mandate in 1994, but Democrats don't now:
There is another difference, though, between 1994 and 2006. In 1994, the Republicans ran on a platform, the Contract with America. Their victory therefore gave them a mandate, notwithstanding that many voters were vaguely aware (if at all) of the Contract. This year, the Democrats ran as non-Republicans. They made a deliberate decision not to take an issue on the biggest issue of the day, the Iraq war, and they downplayed (at least in competitive races) their intention to raise taxes and take other unpopular measures.
Let me get this straight. In 1994, Republicans had a mandate even though most voters barely knew that the Contract with America existed. Why? Because they "ran on a platform." But Democrats didn't run on a platform this time. Why? Because they didn't "take an issue" (I think he means position) on Iraq and "downplayed ... their intention to raise taxes and take other unpopular measures."
There are so many problems with this reasoning it's hard to know where to begin. Why would we believe that the GOP got a mandate in 1994 when their platform was largely unknown to voters? By that standard, the House Democrat manifesto "A New Direction for America" has a plausible claim to a mandate even though voters knew almost nothing about it. Did Democrats downplay or ignore divisive issues like how to deal with Iraq and how to restore fiscal balance? Of course. But the House Republicans certainly didn't emphasize their intentions to cut planned Medicare spending or take other unpopular steps during the 1994 campaign.
In a larger sense, the whole mandate debate can't be resolved because there is no objective definition of the term. Anyone who has studied social choice theory knows that aggregating individual preferences over policy choices is nearly impossible. As I wrote back in 2004, the best work on mandates in political science defines them as a social construction -- essentially, a collective interpretation of election results that carries an informational signal to nervous incumbents worried about re-election. That doesn't make them any less real as a political phenomenon, however. If people believe a mandate exists, it appears to matter. This time around, though, almost no one is actually arguing that Democrats have one.
Update 11/13 8:23 AM: OpinionJournal's Brendan Miniter makes a similar claim:
This year Democrats benefited from a voter rebellion against the GOP. But the party did not win a mandate for its legislative agenda, for the simple reason that Speaker-to-be Nancy Pelosi and others did not lay out their own Contract With America.