Is Europe now seeing NATO as essential since Trump began criticizing their participation?

Victor Davis Hanson:

It is a bit rich to hear Europeans insist that any Trump Administration doubts about NATO’s usefulness is heresy—given their occasional popular indifference to and ambiguity about the alliance.

In current journalistic groupthink, Donald Trump has endangered NATO by suggesting a) it does not have a clearly defined role and needs to find one for the 21st century; and b) the vast majority of European members have welched on their defense spending commitments, on the expectation that the U.S. defense budget would always take up the slack, protect Europe, and thus indirectly subsidize the European social welfare project.

No one really disputes the logic of Trump’s criticisms, only his supposed recklessness in daring to be so rude as to voice them.
...
A European solution at a time of a strengthening euro and widespread loathing of George W. Bush was greater autonomy. The long overdue reification of an all-European Union defense agreement (“Common Security and Defence Policy”), would work side-by-side with NATO, but in truth draw indirectly European resources from it and eventually supersede the transatlantic alliance. We are still waiting to see the fruition of a European External Action Service; so far there are lots of impressive acronyms for various forces and programs, but no brigades in action.
...

There is much more.

Europe in many cases has been free riding on US defense spending for decades.  The US will still supply the bulk of the defense cost under Trump, but it is going to have to spend more of its own resources on defense.  I think Trump is right to push them on this issue.