(CNN)The struggle to uproot the Affordable Care Act shows why it has grown so difficult for either party to sustain the unified control of the White House, the House and the Senate that Republicans now enjoy.
Why one-party government doesn't last
The GOP's health care drive has demonstrated the obvious benefit of one-party government: it has allowed President Donald Trump and Congressional Republicans to advance a top party priority to the brink of passage without meaningful concessions to Democrats, or even to the key health care interests, from doctors to hospitals.
But the debate is also exposing the risk coiled in that opportunity. By removing any effective constraints, unified control has lured Republicans into an ideological overreach. They have produced a deeply partisan health care plan that has provoked intense opposition from most voters and interests outside of their coalition-and even unnerved enough moderate and mainstream Senate Republicans to stall its progress.
If Senate Republicans resolve their disagreements and pass their repeal plan, they could provoke an eruption from the preponderant majority of Americans who consistently express opposition to it in polls. But if they remain deadlocked and fail to repeal the ACA, they will disappoint the base supporters they are hoping will turn out in big numbers during next year's midterm election.
For at least the past quarter century, every time one party has controlled both the White House and Congress it was exactly that combination -- a backlash from voters outside of their coalition compounded by disappointment from voters within it -- that cost them their hold on power. That scenario now threatens the GOP grip on at least the House of Representatives in 2018.
Unified control of government, by either party, has become much more the exception than the rule. From the 1896 election through the 1968 election, one party simultaneously controlled the White House, the House and Senate for 58 of those 72 years. Twice during that long stretch, one side held unified control of the White House and Congress for 14 consecutive years: Republicans under William McKinley, Theodore Roosevelt and William Howard Taft from the election in 1896 to 1910 and Democrats under Franklin Roosevelt and Harry Truman from the election in 1932 to the election in 1946.
Those days are gone. One party will hold unified control of the White House and Congress for just 14 of the 50 years from 1969 through 2018 (assuming, as is virtually certain, Republicans maintain the White House and Congress through the midterm election.) Over that half century, no party has maintained simultaneous control for longer than four years-during Jimmy Carter's presidency and the middle years (2003 through January of 2007) of George W. Bush's.
Bill Clinton and Barack Obama each arrived in office with unified control, just as Trump has, but then lost it in their first midterm elections (1994 and 2010, respectively). In fact, counting 2006, when a voter backlash against Bush swept Democrats to majorities in both chambers, each of the past three times when one party held unified control heading into a midterm election, the voters have revoked it.
Theories have evolved on why unified control of government has become more rare. From 1969 through January of 1993, the shift seemed to reflect a process of incomplete realignment among voters. Over that period, Republicans held the White House for 20 of 24 years but never won the House and controlled the Senate for just six years. Explaining the pattern, political scientists pointed to divided loyalties among Southern evangelical white Christians and Northern blue-collar white ethnics who increasingly rallied to GOP presidential candidates, but retained their traditional allegiance to Democrats for Congress. Indeed, during this period, the share of voters who split their tickets between Congressional and presidential races reached the highest level since World War II.
Divided government has remained common since the 1992 election, but its polarity has reversed. From Bill Clinton's election that year through 2018, Democrats will have controlled the White House for 16 of 26 years, but the House for only six years. The parties have split Senate control almost exactly in half. In this period, the principal explanation for divided government has been an excessive concentration of Democratic votes: while the party's dominance of major metropolitan areas has allowed it to win the presidential popular vote six times in seven elections (and even the Electoral College four times) its inability to compete beyond diverse, culturally cosmopolitan urban centers has limited its reach in both the House and Senate.
But the Congressional debate over the highly contentious health care bill points to another reason why neither party lately has sustained complete control for very long. In an era of intense polarization, unified government unavoidably steers the governing party toward the demands of its most ideological elements, infuriating the other party and unsettling swing voters. The more the party in power accomplishes the more it antagonizes the voters outside of its coalition; meanwhile, its own voters are often discouraged by the compromises and setbacks that inevitably accompany governing. Call it the paradox of unfettered power.
Democrats suffered from this paradox when they enacted the ACA (and other Democratic priorities) under President Obama only to lose control of the House in the next election. Now Republicans could be courting the same type of backlash for their efforts to repeal the law seven years later under President Trump.
Bill Clinton faced that combination of a disgruntled base and energized opposition after he failed to pass universal health care, but did pass a budget plan that raised taxes. George W. Bush confronted a similar equation in 2006 after failing to pass legislation restructuring Social Security-and doggedly persisting in the Iraq War despite mounting public opposition. Barack Obama's early legislative successes-a giant stimulus plan, Wall Street regulation and, above all, the Affordable Care Act ignited the Tea Party uprising but still left many Democrats grumbling in 2010 about what wasn't achieved (a "public option" in health care or breaking-up the biggest banks).
On issues from the budget and taxes to the environment, Trump's agenda likewise is inspiring ferocious opposition from the Democrats and deep doubts among independents. The warning signs are especially glaring on health care. In polls, the legislation consistently faces overwhelming opposition from Democrats and independents and usually ekes out positive support only from a plurality, and not even a majority, of Republicans. Even most non-college and older whites -- two pillars of the GOP coalition -- opposed it in recent polling by the non-partisan Kaiser Family Foundation.
Trump's visceral connection with elements of the Republican base -- particularly blue collar, non-urban and evangelical whites -- might allow him to avoid the turnout slump that contributed to Clinton, Bush and Obama losing control of Congress during midterm elections. But Trump, by aiming his agenda so narrowly at conservative priorities, is fueling precisely the kind of pushback from voters beyond his base that quickly ended those earlier episodes of one-party government. So long as Trump and his congressional allies steer by those limited lights, they will face the same paradox as their recent predecessors in unified control: the more legislative success they accumulate, the more they compound their political risk.