"Denmark couldn't sustain its >20% wind power in its grid without those long transmission links."

Denmark and long? Denmark can't have a "long transmission" in US terms.

Scott's "apples and oranges".

Denmark is less than twice the size of Ted Kennedy's tiny little insignificant Massachusetts.  Denmark is about 1/10th the size of California.
From wiki: A perfect circle enclosing the same area as Denmark would have a circumference of only 742 kilometres (461 mi).
That's little more than half the driving distance from California's southern to northern borders.
The Hoover dam's transmission lines (circa 1935!) carry power to L.A. 462 kilometres (287 miles), or about twice the diameter of that Denmark circle.

I drive 1050km (650 miles) to visit my sister.  I only cross 3 states borders, because she lives just past the last one.
I drive 1100km (700 miles), then go another 300km (200 miles) in a sea-plane to go fishing.
Once I drove 1700km (1050 miles), in one day, to Disneyland. (now we fly!)
My father-in-law drives 3550km (2200 miles) to see his son.
Gosh.  I drove more than 461 miles so my wife could meet Steven King for a couple hours.
Those distances are one way.

In 2006 (BTS numbers), the US had 13,551,624 lane-km (8,420,589 lane-miles) of roads.  Most of it has 'wires'.

Rewiring the US is going to take a lot of wire.  And money.
That's all I am saying.