Delightfully roiling the metaphors, Carl Hulse writes in the NYT:

Momentum, the holy grail of political campaigns, is evidently spreading through the Democratic presidential candidates like the flu.

You'd think the Presidency itself would count as the holy grail. (Maybe drop the "holy" part.)

And if it's something to be desired, how is it like the flu? The point is everyone wants momentum, but what's "spreading ... like the flu" is claiming to have momentum. Once again, writers like to cram a lot of material into a single sentence. Writing two sentences is something they resist like the flu, which is not as bad as the plague.

"We have a ton of momentum," said a spokesman for Representative Gephardt, of Missouri.

Seems like a ton would weigh you down.

More from Hulse:

Candidates crave momentum and hope to ride it like a wave. The problem is that it is difficult to gauge who is actually moving forward and who is engaged in wishful thinking. The laws of physics would seem to preclude everyone from having momentum simultaneously.

I'm no physicist, but it seems to me that if Kerry, Gephardt, Dean, Edwards, and Lieberman tucked into the summersault position at the top of a hill, momentum would simultaneously favor them all. They could all also "ride ... a wave" simultaneously, and I for one would be interested in following their choice of surfwear.

Hulse also treats us to a great old momentum quote--from Old Bush:

It was the first George Bush who shook hands with what he called "Big Mo" after he won the Iowa caucuses in 1980. "I suppose I am out of the pack," he said in a classic bit of political analysis, "but they will be after me, howling and yowling at my heels. What we will have is momentum. We will look forward to Big Mo being on our side, as they say in athletics."

I pause for a moment of Old Bush nostalgia. Who else could talk like that, coming up with "Big Mo," then calling sports "athletics"?