Why another shutdown? Our government has three political parties these days: Democrats, Republicans and the new "radical Republicans."

That radical Republican label has some history. The old radical Republicans were the Grand Old Party's progressive wing. They were opposed during the Civil War and through Reconstruction by the party's liberals and conservatives.

They strongly opposed slavery, demanded harsh policies against ex-Confederates, and pushed civil rights and voting rights for newly emancipated slaves. Abraham Lincoln and other moderates sought compromise and unity for the party and the nation. Today's radical right would probably call Lincoln an appeaser or a "RINO — Republican in Name Only."

Today's radical Republicans are quite the opposite in ideology, if not in temperament, from the originals. Today's tea party-era radicals call themselves "conservative," but they radically challenge, block and overturn established laws, policies and traditions that get in the way of their ideological goals — even if it means a federal government shutdown or a possible default of the nation's debt obligations.

Long-running partisan battles over taxes, spending, deficits, the debt ceiling and other fiscal concerns have come to a head this season in pitched, last-ditch battles by Republicans to block, repeal or defund the Affordable Care Act, better known as Obamacare.

Democrats believe that their hard-won Obamacare law — having survived congressional opposition, the U.S. Supreme Court and a presidential election in which it was a central issue — should be given a chance to work.

Republicans like Texas Sen. Ted Cruz fear that once Obamacare kicks in, as he told Fox News' Sean Hannity in July, it "will never, ever be repealed" after Democrats "get the American people addicted to the sugar."

In other words, if people get a chance to try Obamacare, they might like it as much as they like Social Security, Medicare, Medicaid and other programs long decried by conservatives as socialistic.

Republicans have a right to hold objections to programs they don't like. But conservatives do their country a disservice by holding the normal functions of government hostage to their tests of ideological purity. That's not just coming from me. It also comes from many of their fellow conservatives.

Some of the party's best known conservatives have come under attack from the GOP's tea party wing for failure to be conservative enough. The Senate Conservatives Fund, for example, has been running ads that attack Republican Sens. Jeff Flake of Arizona, Richard Burr of North Carolina, Lamar Alexander of Tennessee and Thad Cochran of Mississippi. Their sin: reluctance to support their party's self-destructive strategy against Obamacare.

"Tell Senate Republicans to stand with Ted Cruz and (Utah Sen.) Mike Lee," says the group's website, "not (Senate Minority Leader) Mitch McConnell (of Kentucky) and (Senate Minority Whip) John Cornyn (of Texas)."

Other conservative groups, including the Tea Party Patriots, For America and Heritage Action, have mounted ads attacking Republicans in both houses who don't rigidly support their efforts to defund Obamacare.

Over on the House side, Cruz thumbed his nose at traditional protocols by plotting strategy with tea party House members — against Speaker John Boehner's wishes.

What is Boehner to do? He's been warned by tea partyers that he'll be voted out of his speakership if he passes any major legislation with votes by less than a majority of House Republicans. The radical right may be a minority of the House, but they appear to leverage a majority of the power against Boehner's lack of a counterstrategy.

Cruz has taken de facto leadership of the new radical Republican assault on Obamacare, most visibly by speaking for 21 hours and 19 minutes in a pseudo-filibuster about his objections to the program. This won soaring support for him in the party's right wing, setting him up for what most likely will be a presidential run in 2016. One wonders whether he cares more about Republicans or the Ted Cruz Party.

So far, the strident GOP push to overturn Obamacare, even as Americans in need of health care sign up for its state insurance exchanges, shows Republicans to be holding on to the same self-defeating strategy that helped the party lose the 2012 presidential race: talking ceaselessly to themselves.

Worse, they're arguing among themselves, giving us two Republican parties as if one isn't enough.

Clarence Page, a member of the Tribune's editorial board, blogs at chicagotribune.com/pagespage.

cpage@tribune.com

Twitter @cptime