Here's a list of what I predict will happen (with no particular order):

• Billions of tax payer's dollars would be wasted. The Bitcoin network would continue operating, as the state cannot endlessly retain this attack, because it doesn't have the money.
• People would likely consider Bitcoin transactions prone to reversal for quite a lot of time.
• If this happens in the far future, then perhaps the government that attempted to do it will be sanctioned by other governments that save / invest in Bitcoin.
• Some people will take advantage of their transactions being unconfirmed and double-spend them.

Here's a list of the reasons I think this is unlikely to ever happen:

• It'd require an astonishingly efficient coordination between the government people. And usually, they don't work efficiently, because... they're bureaucrats.
• It'd require vast amounts of money such that they'd be more incentivized to issue and earn the number #1 asset in the world.
• They would have to purchase an unusually large number of ASICs, and setup a noticeably long infrastructure. I don't believe there even exist so many ASICs, so they'd probably be forced to manufacture their own.

Did I mention that bureaucrats do not work efficiently?