There's "concern" and then there's "urgent" concern.
There is not a single democrat politician that views China as an urgent concern.

Most of them view China as an urgent concern. They don't necessarily share the view that firing up the Pacific Fleet to "take action in a real way" is the right way to address that urgent concern. China's a major threat that needs to be contained using a lot of different tactics and measures - and not everyone's going to agree with them. You think the Navy needs upgrading? Okay - and others think that a massive commitment to defending Ukraine and an equally unambiguous commitment to Taiwan's defense are also essential elements to make sure that China doesn't get the wrong idea about whether the West is serious about stopping them from following Russia's lead in trying to reclaim "their" historical land.

Disagreement about the priorities and methods of countering a threat is not the same as disagreeing that the threat is real and "urgent."

Why are you assuming that selling us Greenland is the real goal? Can we even afford it?
Why not get the Danes to make upgrades in certain areas, upgrades that are mutually beneficial in terms of trade and security?

I'm not assuming that - it's simply the only goal that Trump has assert. So he's antagonized our allies and declined to rule out the application of military force against a fellow NATO member for the sole stated purpose of trying to get Greenland.

And the Danes? Seriously? The 26th largest country in Europe? What possible "upgrades" in our Danish trade and security are you talking about that are worth antagonizing all of the EU and NATO like this? That they might increase their military spending to 2% of GDP, which would be an increase of....nothing, because they're already at 2% of GDP?

There's nothing the Danes have that is of any material security interest to us except possibly Greenland.