I've seen two lines of skepticism about the idea that bridgegate is really all that damaging to Chris Christie's 2016 ambitions, and I think they're both wrong. One line of argument notes, correctly, that scandals are eminently survivable when they hit otherwise-popular politicians with otherwise-unpopular antagonists. The other line of argument notes, also correctly, that voters tend to be fairly myopic and there's no real reason to think the 2016 electorate will care much about something that happened in 2014.
Both true, but fundamentally wrong. The relevant things about the 2016 primary are that it's happening right now and that it's really hard to win.
It's happening right now in the sense that in order to win, any candidate needs to first gain the allegiance (or at least nonhostility) of a wide range of elites outside his immediate political circle. House members from South Carolina. State senators from Iowa. Anti-abortion activists in New Hampshire. Talk radio hosts. Fox News executives. Donors. Lobbyists. State-level Chamber of Commerce chiefs. These people are paying attention right now, and they're thinking about who they want to back and who they want to bandwagon against. And there's just no way this bridge thing is making any of those people more likely to support Christie than they were six months ago. Republican elites are mostly looking to find a candidate who is both conservative, effective, and electable and this makes him look less electable and less effective without making him look more conservative. It's bad news.
Which gets us to the other point, namely that it's very hard to win. Conservatives like Paul Ryan. Conservatives also like Scott Walker. But they can't both be the nominee! In fact, since they're from Wisconsin, they probably can't even both be serious contenders. Only one person gets to be the nominee in a country that right now has a lot of second-term Republican Party governors and a former VP nominee alongside the usual smattering of senatorial wannabes.
That's just a tough landscape for candidates. For party elites, by contrast, it's an embarrassment of riches. You get to be quite choosy, so every stumble counts for a lot.