Twice, the politics of the September 11, 2012 Benghazi attack has backfired on Republicans. Three years ago, presidential nominee Mitt Romney stalled his own momentum from the first debate when he challenged Barack Obama on whether the president had called the attack an “act of terror” the following day, and got a bracing fact-check from the moderator.

Three years later, the Republican-led House Select Committee on Benghazi served Hillary Clinton an 11-hour testament to her stamina, resilience and competence. If the gushing media coverage is any indication, her poll numbers may get another boost this week, disproving the earlier contention of House Majority Leader Kevin McCarthy.

The failure of Benghazi to take down either Obama or Clinton should not have surprised anyone. Presidential scandal politics almost never pay off for the opposition party.

Six months after the Abu Ghraib torture revelations surfaced, President George W. Bush won re-election with a larger popular vote share than in his first race. The same was true for Bill Clinton in the aftermath of Whitewater, Travelgate and Filegate. House Republicans’ headlong pursuit of impeachment led to Democratic gains in the 1998 midterms, precipitating the fall of Speaker Newt Gingrich.

In the decade that came before, Ronald Reagan had shrugged off first-term scandals involving cabinet officials to win re-election easily. After Democrats conjured up a Republican “sleaze factor” theme, Reagan carried 49 states in 1984. The Iran-contra scandal was a bigger challenge—a special prosecutor’s report would eventually hurt George H.W. Bush in 1992—but by that time Reagan had forged a historic arms control agreement with the Soviets, helped George H.W. Bush win the presidency, and left office with high personal popularity and job approval ratings.

Yet opposition parties can’t help themselves when the whiff of scandal is in the air. Like a gambling addict, politicians always want to bet the next scandal is going to come up “Watergate.” During the Obama presidency, Republicans have never left the scandal casino, no matter how many times the (White) house won.

Conservatives wasted no time once Obama was sworn in. Michelle Malkin rush-published her literary hit job, “Culture of Corruption,” six months after he took office. The book failed to make a dent in the president’s reputation, but it whetted conservatives’ appetites. By 2011, Republicans were spending a lot of time fanning the flames over Solyndra and “Fast and Furious.”

But no one could ever prove that the failed solar panel manufacturer received special favors from the government. Nor could they get traction on the goofy theory from some right-wingers about a White House conspiracy to secretly flood Mexico with American guns so Obama could build support for gun control legislation.

Despite the long record of failure, the Republican scandal sleuths refused to quit in Obama’s second term. In 2013, conservatives convinced themselves that Obama directed the IRS to harass Tea Party outfits. But the flap faded in the absence of proof that the IRS was deliberately treating conservative organizations worse than others. Last Friday, the Justice Department closed a two-year investigation without filing any charges, concluding any excessive scrutiny was due to institutional disorganization, not politics.

Good-government types may huff: Well, why should Republicans give up? Congress has a responsibility to exercise oversight of the executive branch. It has every right to conduct independent investigations and not accept other institutional findings at face value.

All correct. Honest, independent congressional investigations are a necessary component of our system of checks and balances. But pursuing the truth without fear or favor also means not fearing your own political base. It means accepting all the data instead of cherry-picking it. It means embracing reality even when you fail to find hard evidence of criminality or ethical lapses.

What the obligation to conduct oversight doesn’t mean is theatrical grandstanding and political gamesmanship. It doesn’t mean assuming the worst of your political opponents and never stopping until you prove it.

The Machiavellians might say: facts, schmacts. As a matter of raw politics, what’s the downside to scandal-mongering? Sure, the odds are low that you’ll find a smoking gun with the president’s fingerprints. But even if the opposition comes up empty, what has been lost? If the executive branch has to spend months battling bad poll numbers and satisfying congressional investigators, at the expense of its policy agenda, that’s at least a partial victory for the opposition.

But recent experience reveals the downside. Though the executive branch may become distracted, so can the opposition. While obsessing over imagined cover-ups, Republicans have neglected the essential task for an opposition party of developing an alternative policy agenda that can impress voters and shape the debate.

Scandals always raise questions about individual character and competence, but they don’t always raise questions about the merits of the parties’ ideology and policy positions. Since the George W. Bush presidency ended on the twin failures of the Iraq War and the market crash, Republicans have needed to regain credibility for their conservative worldview. Chasing Obama and Hillary Clinton scandals doesn’t help solve that problem.

There’s a reason why in the most recent ABC/Washington Post poll, President Obama’s approval rating was a 51 percent, while the Republicans in Congress were stuck at 24 percent.

Paul Ryan appeared to acknowledge the problem last week, telling his caucus, “We need to move from being an opposition party to being a proposition party.” Yet he also responded to the Justice Department’s closing of the IRS investigation with a defiant pledge of continued scrutiny from the House Ways and Means Committee. Scandal politics are hard to quit.