To tolerate something means putting up with it, enduring it. It's an act of forbearance. It does not mean acknowledging or liking something, but essentially ignoring it. It's a refusal to take sides, a "don't know" in pollster-speak. But in political discourse the word is often used to imply a positive act of engagement and acknowledgement, even of limited sanction. If intolerance is a dislike, then tolerance is treated as a qualified like.
An example of this is gay marriage, which is regularly presented in binary terms as something one must either be for or against. As Chris Dillow has noted, the debate is framed as one of equality and therefore something that affects us all, though in reality most people are either wholly indifferent or in the "I don't see why they shouldn't" camp. The Catholic writer Timothy Radcliffe recently provided a good example of how tolerance can be used to defend prejudice: "Many Christians oppose gay marriage not because we are homophobic or reject the equal dignity of gay people, but because 'gay marriage' ultimately, we believe, demeans gay people by forcing them to conform to the straight world". He goes on: "Tolerance means, literally, to engage with other people who are different. It implies an attention to the particularity of the other person, a savouring of how he or she is unlike me, in their faith, their ethnicity, their sexual orientation. A society that flees difference and pretends we are all just the same may have outlawed intolerance in one form, and yet instituted it in other ways". The argument deployed here against gay marriage is not that it is a theological impossibility (something that we cannot tolerate, even if we wished to), or a moral abomination (something that we choose not to tolerate), but that its toleration would obliterate the separateness that gays insist upon. Such sophistry makes you wonder if Father Radcliffe deserves a transfer from the Dominicans to the Jesuits.
An example of the word being used correctly is Barack Obama's insistence, in response to the Sandy Hook Elementary shootings, that: "We can't tolerate this any more. These tragedies must end. And to end them, we must change". In other words, the US can't go on ignoring the consequences of liberal gun laws. "We cannot accept events like this as routine. Are we really prepared to say we are powerless in the face of such carnage? That the violence visited on our children year after year is the price of our freedom?" Obama has already been criticised for not explicitly mentioning "guns" in his speech, as if anybody could honestly infer that he is arguing for teachers to be armed to the teeth, while others have upbraided him for his hypocrisy in tolerating the death of children as the collateral damage of drone strikes, though it is hard to see how a charge of double standards (however legitimate the charge may be) is anything other than a distraction in relation to US gun control. If Obama is open to criticism, it is that he avoided all mention of guns during the presidential election, though you can probably see the tactical logic from his perspective. In other words, he displayed tolerance of the carnage, as a relative political priority, on the hustings.
For that reason, it is doubtful that the current tragedy will lead to major reform unless there is a clear shift in the mood of the US public. For a variety of reasons, excellently outlined by Jill Lepore in the New Yorker back in April, this is likely to be a gradual change, not an overnight conversion. The roots of the gun control debate lie in the 1960s push for civil rights. The conservative reaction to this in the 1970s, the focus on liberty over equality, recast the constitutional requirement to maintain armed states militias as a right of the individual to carry a gun. Pro-gun became a badge of identification for conservatives. Though gun ownership has actually been steadily declining since then, the gun-owning minority have become fiercer in defence of their right because of its political symbolism. The recent post-election predictions of demographic irrelevance for angry white men are likely to make them even more embattled.
Gay marriage will become legal because the majority of the population simply aren't fussed, while those that are passionately in favour have strong arguments (equality, fairness) and those that are passionately against have weak arguments (theology and a too-obvious obsession with sex). The basis of our tolerance is disinterest. In contrast, US gun control is likely to inch forward at best, despite a growing majority in favour of tighter regulation. The emotion over Sandy Hook will dissipate, just as it did after Columbine and similar shootings. Occasional tragedies will be tolerated until gun-ownership goes out of fashion as an identifier of personal liberty. Given how embedded the idea is in American popular culture, and how much spadework the pro-gun lobby groups have put in over the last 40 years, that won't happen on Obama's watch.