Why are Senate Republicans scrambling to pass a hastily rewritten tax bill that most Americans don't even like? Think of it as the mirror image of what Democrats did seven years ago with the Affordable Care Act. When it's a core issue for your party — as tax cuts are to Republicans, health care was to Democrats — you'd better be able to pass it.

The bottom line: When Republicans control the White House and both chambers of Congress, it would be hard to explain why they couldn't pass a rewrite of the tax code — every bit as central to their agenda as health care was to the Democrats when they controlled the White House and Congress. The details, and the polling, are almost beside the point.

The parallels between the tax bill and the Affordable Care Act are hard to avoid:

President Trump has been promising the tax bill since day one, and Republican leaders have been campaigning for tax cuts for years.

Barack Obama campaigned on the health care for the uninsured, and Democrats were eager to finish what they regarded as the last missing piece of the social safety net.

Trump and Republicans are especially eager to pass the tax bill after the embarrassing failure of their last major initiative (repealing the Democratic health care law).

Democrats were eager to pass health care after decades of failures, including the collapse of Bill and Hillary Clinton's health care effort in 1994.

A Republican president and Congress give them the best shot at tax cuts that they're going to get, just as Democrats knew they'd never get a better shot at health care than they had in 2010.

The polling is historically bad for the tax bill — but it was for the health care bill too, by the time Democrats were ready to pass it. Republicans are going ahead with the tax bill because they know it's popular with a majority of their voters, just as health care was with most Democratic voters.

Where they're different:

Senate Democrats rewrote their health care bill on the floor — largely behind closed doors — to get enough votes. That's what Republicans are doing now. But the Democrats took days, while the Republicans are doing it in just hours.

A former Senate Republican aide who worked on the health care bill notes that the rewrite by Senate Democrats took "the entire month of December" (here's a good recap from The Washington Post). The Republican tax bill rewrite happened overnight.

The Democrats finished their health care bill through the budget "reconciliation" process, which only required 51 Senate votes. But that happened after the Senate passed its initial version with 60 votes — and then had to make the final tweaks through reconciliation after Democrats lost their 60-seat majority. Republicans are using the process from beginning to end.

What to watch: Remember how Democrats took the blame for everything bad that happened with health care after they passed the ACA by themselves, and had trouble getting any credit for the good stuff? If Republicans rewrite the tax code by themselves, they're going to own it, too.