the proverbial dog that caught the car. とはどういう意味ですか?

質問を翻訳

What does "the proverbial dog that caught the car." mean in the last sentence?

As Republicans take power in Washington, their first priority is trying to figure out what to do about the Affordable Care Act. They have ferociously demonized the policy since the moment it was passed, voted to repeal it dozens of times in the House, and promised over and over that it would be abolished the second they take power.

But as Jonathan Chait notes, they're running into some sticky realities, most notably the fact that about 20 million people have gotten health insurance coverage under the law. If they do a flat repeal, the political backlash will be spectacular — and none of their policy ideas have the faintest chance of delivering anything better. Republicans are flailing around like the proverbial dog that caught the car.