It is common these days in Washington to portray the Republican Party as facing potentially existential dangers stemming from the outlandish influences of its Tea Party contingent, its strident opposition to President Obama’s liberal leadership, and underlying demographic trends in the country. And it is true that the Republicans face serious challenges, internal and external, that aren’t going away anytime soon.

But the Republican Party isn’t the party most in danger of a political blowout over the next three years. That distinction belongs to the Democrats, and it can be seen in a fundamental reality of America’s two-party system—namely, nothing devastates a ruling party as surely as a failed presidency.

This is not to say that Obama’s second term will be a failure. It’s too early for such a judgment. But the signs of failure are evident, perhaps most clearly in the perceptions of congressional Democrats facing reelection next year. It appears that some are beginning to put daylight between themselves and their president. Louisiana senator Mary Landrieu flew to her home state with Obama on Air Force One last week, but once they landed, according to the Wall Street Journal, she was too busy with other commitments to accompany the president during his state visit. The paper also reported that Obama met recently with Senate Democrats facing reelection and heard complaints about the rollout of his healthcare legislation and its impact on the nation’s political climate.

The reality that nothing devastates a ruling party as surely as a failed presidency is written indelibly in the country’s recent political history. Consider the Democratic fate in 1968, after Lyndon Johnson’s failed presidency—reflected in a devastating war that seemed out of control and impossible to win; racial and student riots that generated significant numbers of deaths in the streets; the threat of economic dislocations. The voters inevitably turned to opposition Republicans to clean up the mess. Thus did Richard Nixon become president.

Then there was the Nixon mess of 1973-1976—Watergate, the most unnerving political scandal in the country’s history; disruptions in the marketplace wrought by Nixon’s wage-price controls; a recession that spawned persistently high unemployment. The country not only repudiated the GOP presidential ticket in 1976 but also devastated the party’s congressional standing in 1974, reducing its House ranks by forty-three members and its Senate ranks by three. In 1976, the country turned to Jimmy Carter, who captured the national mood by promising the American people he would never lie to them.

But Carter proved unequal to the task of governing the country, manifest in runaway inflation and persistently a sluggish economy (the brew known as "stagflation") and in his weak leadership in the face of major foreign challenges. And so the American people repudiated him and his party at the next election. Carter carried only six states and the District of Columbia and captured just forty-nine electoral votes to Ronald Reagan’s 489. Meanwhile, Democrats lost thirty-three seats in the House and twelve in the Senate, which came under GOP control for the first time since 1953.

And then there is Obama himself, elected in 2008 largely because of the tarnished Republican image after President George W. Bush’s second term, a failed presidency by any measure. This was evidenced by a misguided Iraq adventure that was initiated on the basis of false intelligence and which mired the United States in a bog of chaos that it could neither control nor escape. Add to that the runaway fiscal policies of the Bush years, culminating in the financial collapse of 2008 and the most horrendous economic plunge since the Great Depression.

Obama may believe he won the subsequent election based on his sparkling public persona and the overwhelming wisdom of his policies, and they no doubt contributed to his getting the 2008 Democratic nomination. But his general-election victory came to him primarily through the fundamental political reality in American politics that presidential elections are won or lost based, more than anything else, on the record of the incumbent. Bush’s second-term record was sub-par, which meant that no Republican that year was going to beat any Democrat.

Is the current presidential-election cycle shaping up similarly, only with the Democratic incumbent ushering in a new GOP surge? Based on Obama’s performance in this first year of his second term, such a prospect can’t be discounted. And it isn’t just the performance, but also the president’s approach to his job these days. He seems disengaged, airily disconnected from the fray, contemptuous not only of his GOP opposition (a counterproductive attitude in itself) but somewhat contemptuous of the whole political game.

That may be why some polls are picking up a significant new development in Obama’s standing with the electorate. In the past, as his approval ratings fluctuated, his "personal-favorability ratings" remained solid. Thus, even when the American people weren’t happy with his governance, they still liked the man himself. This kind of personal popularity can help presidents weather the tough times of their tenure, as it did for Obama through his first term. But now, according to a late-October Wall Street Journal-NBC poll, only 41 percent of respondents viewed Obama in a favorable light. Fully 45 percent held negative views of him as a person.

Meanwhile, his approval rating—how the voters view his performance in office—fell to just 41 percent in a recent Pew survey, down 10 percentage points since May. History tells us that such an approval rating, if it persists, constitutes dangerous political territory for a president and his party.

These numbers doubtless are a reflection to a significant extent of the reality that Obama is on the losing side of the most powerful issue facing the country today—the persistent and accumulating problems associated with his healthcare legislation, colloquially known as Obamacare. As this political drama unfolds, it is becoming increasingly clear that this is not merely a software botch that can be fixed through a technology remediation. Obamacare is going to transform Americans’ health-care experiences in profound ways, many of them as yet unforeseen and some of them vexing to large numbers of citizens.

That helps explain the debilitating political impact on the president of the discovery that he was not speaking correctly when he promised the American people that, under Obamacare, they could keep their health insurance if they liked it. It now turns out that, for millions of Americans, that isn’t true. And there is reason to believe this was understood by administration officials when they were pushing this high-impact legislation through Congress without any bipartisan cooperation.

Add to that the appearance of presidential haplessness in foreign affairs, particularly in Obama’s zig-zag policy initiatives related to the brutal civil war in Syria—first demonstrating a strong aversion to getting involved; then proposing military support for the Syrian rebels in response to the apparent use of chemical weapons by the Syrian regime; then turning another about-face when Russia sought international cooperation for an effort to get the regime to relinquish its chemical armaments.

Given all of this, the president’s command of events has been lost, at least for now. And, if this situation persists, he could lose his ability to produce the kind of second-term record that bolsters his party in coming elections. This represents the kind of political weakness that breeds problems for incumbent presidents and retards their ability to deal with them successfully. A serious foreign-policy adversity for America, a sudden economic downturn, a lack of any serious accomplishment on the domestic front, persistent problems with Obamacare and droning new discoveries of its disruptive impact on Americans’ lives—these are the kinds of problems that render a presidential term a failure.

If such problems emerge and persist, the voters will turn to the opposition party by default, notwithstanding the Republicans’ own difficulties and limitations. That’s how our two-party system works, and the marvel of it is in its resilience—for the parties themselves and for the system as a whole. Thus, if Obama manages to pull out of his current tailspin, Democrats will remain politically viable at both the congressional and presidential levels, and Republicans will remain stymied in their efforts to chart a new course for the nation. But he may not be able to turn it around, and that prospect looms as the single most serious party vulnerability on the scene today.

Robert W. Merry is political editor of The National Interest and the author of books on American history and foreign policy. His most recent book is Where They Stand: The American Presidents in the Eyes of Voters and Historians.