The government shutdown because Republicans won’t negotiate with Democrats to keep it open. As Alex Shepherd in the New Republic points out:

The Democratic demands to keep the government open were straightforward and reasonable. They wanted to extend Affordable Care Act premium subsidies that will expire at the end of the year thanks to Trump’s One Big Beautiful Bill Act, which would prevent health care costs from skyrocketing for millions; to claw back Medicare funding that was cut in the OBBBA; and binding assurances that money that has been appropriated by Congress will be spent by an executive branch that has (possibly illegally) refused to do so in many cases.

This would likely result in an exchange for an extension of the ACA subsidies. Of course, Trump is an idiot and could not negotiate out of a paper bag.

This shutdown is really the best play Democrats have against this corrupt administration. They’ve made this move to shine a light on how Trump is basically stealing from the poorest people, usually Red State idiots, to the richest.

If they can make the case to the American public, and it appears to be working, then the shutdown is likely to continue for quite a while.

On the flip side, for Trump and his cronies, they think the shutdown is really just an opportunity to gut the federal government. Of course, he’s been doing that already and failing pretty spectacularly, so it’s not much of a threat.