Think about just how bizarre it is for Republicans to position themselves as the defenders of unrestricted Medicare spending. First of all, the modern G.O.P. considers itself the party of Ronald Reagan  and Reagan was a fierce opponent of Medicare’s creation, warning that it would destroy American freedom. (Honest.) In the 1990s, Newt Gingrich tried to force drastic cuts in Medicare financing. And in recent years, Republicans have repeatedly decried the growth in entitlement spending  growth that is largely driven by rising health care costs.

But the Obama administration’s plan to expand coverage relies in part on savings from Medicare. And since the G.O.P. opposes anything that might be good for Mr. Obama, it has become the passionate defender of ineffective medical procedures and overpayments to insurance companies.

How did one of our great political parties become so ruthless, so willing to embrace scorched-earth tactics even if so doing undermines the ability of any future administration to govern?

The key point is that ever since the Reagan years, the Republican Party has been dominated by radicals  ideologues and/or apparatchiks who, at a fundamental level, do not accept anyone else’s right to govern.

Anyone surprised by the venomous, over-the-top opposition to Mr. Obama must have forgotten the Clinton years. Remember when Rush Limbaugh suggested that Hillary Clinton was a party to murder? When Newt Gingrich shut down the federal government in an attempt to bully Bill Clinton into accepting those Medicare cuts? And let’s not even talk about the impeachment saga.

The only difference now is that the G.O.P. is in a weaker position, having lost control not just of Congress but, to a large extent, of the terms of debate. The public no longer buys conservative ideology the way it used to; the old attacks on Big Government and paeans to the magic of the marketplace have lost their resonance. Yet conservatives retain their belief that they, and only they, should govern.

The result has been a cynical, ends-justify-the-means approach. Hastening the day when the rightful governing party returns to power is all that matters, so the G.O.P. will seize any club at hand with which to beat the current administration.

It’s an ugly picture. But it’s the truth. And it’s a truth anyone trying to find solutions to America’s real problems has to understand.