DC is taxed – but does not have representation in Congress. Its such an established problem their license plates read “taxation without representation”.
Democrats have in the past tried to fix this by working to get them representation, but have failed in their attempts. Partially because of opposition from Republicans concerned that DC will tip the balance in favor of the Democrats.
So a Republican has proposed ending the taxation. How perfectly conservative – drain the federal budget, avoid solving the root problem, further institutionalize the deprivation of voting rights for a group of people who trend Democrat, and snag some stellar PR at the same time.
Expect the Democrats to raise a few lion like mews and maybe put up a kabuki fight, then lose. Or hell, they might actually fight it by pushing back against the specific proposal. Imagine if they had the guts and strength to turn this into an issue of giving the residents of DC representation instead?