Robert Merry sees brighter prospects for the GOP in the near future than I do. He notes that American presidential elections are “largely referendums” on the party in power, and it’s inevitable that either one will mess up sooner or later, yielding the other its turn.

That much I don’t disagree with, and I concur that “strong presidents can reshape their parties just as their parties can bring down weak presidents.” The problem for the GOP is that strong presidents don’t come along with any regularity, and thanks to the errors of the Bush administration, the next Republican president will have to struggle against his party’s present reputation.

The overall brand of a party, as colored by events as significant as a failed war, modifies how much margin for error a president gets. A party that started a war it couldn’t finish is cut less slack for future mistakes, while the other party may get a pass for blunders that would be fatal to its rival. Consider Carter, Reagan, and now Obama and Benghazi.

Carter came to power thanks to the GOP’s missteps. Republicans had blown themselves up with Watergate, and though the country was eager to forget the whole thing, Ford’s pardon of Nixon was an unwelcome reminder. The country was troubled by inflation, Vietnam had fallen to America’s enemies, and a fresh start under a new kind of Democrat—neither a Humphrey nor a McGovern—seemed appealing.

By 1980, Carter had come to be associated with gas lines and other symptoms of economic “malaise.” He had also become a figure of military weakness, something dramatized by the Soviet invasion of Afghanistan, the Iranian revolution and hostage crisis, and the failure of the military mission to rescue the hostages.

My argument is that given the reputation his party had at the time, Carter had no margin for error when it came to foreign policy, and these failures were seen not as aberrations but as characteristic of the weakness of the president and his party. A president whose party had a stronger brand would not have taken so much damage—as Reagan proved.

The Hezbollah bombing of the Marine barracks in Beirut in 1983 cost more American lives, by far, than the hostage crisis and botched rescue. Reagan pulled out of Lebanon—and invaded Grenada, which proved to be a quick, if not quite clean, intervention. It could have been seen cynically as an attempt to distract from the Lebanon debacle; that was certainly how the left saw it. But Reagan didn’t suffer much in the following year’s election for the deaths of over 200 Americans in Beirut or from any suspicion that Grenada was a smokescreen. Why did Reagan emerge unscathed from events that would have destroyed a Democratic administration like Carter’s?

The specifics are not exactly comparable, of course: Carter’s humiliations were seen as part of a deteriorating strategic picture for the U.S. in general, while Reagan’s Middle East debacle was not. But it seems clear that differences in each president’s reputation—a reputation influenced by his party’s overall brand—played as great a role as differences in the world situation in shaping voters’ responses to these setbacks.

The GOP is now in the position that Carter’s party was in, and in contrast Obama has acquired something like Reagan’s “Teflon” coating—as the Benghazi episode illustrates. Benghazi was a national humiliation, caught the administration in a tangle of its own words, and should have raised serious questions about why we were in Libya in the first place. Americans, including an ambassador, had died, and Obama’s signature foreign-policy intervention was the strategic backdrop. It happened shortly before an election, yet Obama took no damage from it. Instead, Republicans who insisted that this was a great scandal came off looking like unpatriotic kooks to non-Republicans. Why?

It’s a simple matter of trust: the nation now trusts Democrats more than Republicans on foreign policy, and Iraq is largely the reason for that. This gives Obama and his party a margin for error: his Benghazi screw-up is seen as an aberration, much as Reagan’s Lebanon humiliation was. It doesn’t fit the brand’s reputation for leadership, and that reputation is stronger in the public mind than the impression made by an incident even as gruesome as the Beirut barracks attack or the murder of an ambassador.

Coca-Cola knows how this works. If a customer gets one flat bottle of pop, he won’t flee from Coke to Pepsi or RC. He may be unhappy with this particular experience, but the brand is strong enough that it shapes a storyline even for the dissatisfied customer: this was a one-off mistake; you trust the brand, and that counts for more than what you see with your eyes or taste with your tongue. Trust trumps experience, up to a point.

The point beyond which trust doesn’t trump experience? A failed war, for one thing.

The larger argument of my “GOP’s Vietnam” article is that failed wars don’t just affect a party’s reputation in foreign policy but have spillover effects elsewhere. If I’m right about that, the GOP has today depleted its margin not only in foreign policy but across the board. And the next Republican president, like Carter, may not get much benefit of the doubt from the public.