Sen. Elizabeth Warren and President Obama are having a bit of a tiff over the Trans-Pacific Partnership. Warren, D-Massachusetts, objected to giving the president fast-track authority to negotiate the deal (which would force Congress to approve it on an up-or-down vote, with no amendments). She helped torpedo that possibility. Obama criticized her, then some of Warren's supporters said his criticism was sexist.

On the policy merits, Obama is right and Warren is wrong. This is what she says about giving the president fast-track: "The president has committed only to letting the public see this deal after Congress votes to authorize fast-track. At that point it will be impossible for us to amend the agreement or to block any part of it without tanking the whole TPP. The TPP is basically done. If the president is so confident it's a good deal, he should declassify the text and let people see it before asking Congress to tie its hands on fixing it."

This is so ludicrous I doubt she takes it seriously. It's plausible pablum for low-information voters, not a legitimate policy argument.

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If Congress doesn't like the agreement, then Congress can vote against it. Giving the president fast-track in no way prevents lawmakers from doing so. All it does is keep them from offering amendments, which Warren puckishly calls "fixing it." (Note: She doesn't mean "fix.")

The reason the president wants and needs fast track is that otherwise it's basically impossible to get trade bills through Congress. The bill will come back with all sorts of amendments that have not been negotiated with all the other people who have been sitting around the table with American trade representatives for long months. Those people will get irate and leave the table if the executive branch tries to go back and say "Hey, guys, just a few small changes." Without fast track, we wouldn't have any trade agreements, because this would be the equivalent of saying that every other country at the table gets one voice on the deal, but the United States gets 536.

Now, maybe Warren thinks the world would be a better place if we didn't have any trade deals with other countries. Maybe she thinks the world would be a better place if we didn't have this particular deal. But if so, the courageous thing to do would be say that, rather than offering to "fix" it.

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Obama said: "The truth of the matter is that Elizabeth is, you know, a politician like everybody else. And you know, she's got a voice that she wants to get out there. And I understand that. And on most issues, she and I deeply agree. On this one, though, her arguments don't stand the test of fact and scrutiny." Some critics found this condescending.

Is it sexist to disagree with Warren? Or to dismiss her position as, essentially, brainless political posturing? I just did, and I am pretty confident that this has nothing to do with the fact that she sports two X chromosomes.

But what about the way he said it, using her first name, disparaging her motives? Sen. Sherrod Brown, D-Ohio, suggested this was sexist. (He's since apologized.) As someone who has written more than once about the disproportionate, and frequently gender- specific, hate that women attract in the public square, this is certainly an argument that I'm ready to believe.

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But not every use of a first name is sexist. Not every political disagreement secretly is about the gender or race of the participants. Sometimes a cigar is just a cigar, and sometimes calling a senator by his or her first name is just, well, calling a senator "Sherrod." Conservatives will attest that Obama does not reserve condescending and dismissive statements about his opponents and their motives for female politicians; this is pretty much par for the course when Obama discusses the Republican Party.

Now, it's true that the president used Brown's first name in a nice way, while he used Warren's in an answer that was pretty dismissive. The great difficulty of sexism in this moment is that we're fighting subtle bias and knotty structural issues, not fellows who stride up to the podium to jauntily announce that women just don't have the brains for politics, the dear little things.

But there's a reason that I rarely dissect a statement in search of such subtle bias. It's because sexism is so serious we need to be careful when and where we level accusations. There's a danger that sexism will become just another magic word, used to shut down debate rather than start a needed conversation. It's a terrible idea to weaponize a serious issue and bring it into garden-variety political disputes; the accuser gains some temporary political advantage at the expense of actually fighting sexism.

People who carelessly toss around the "s" word are trying to have things both ways: They want sexism to be something very, very bad that forces the refs to stop the action and pull you out of the game, and they also want to be able to level this charge at every minor verbal tic that might be sexist. Even if it might just be, you know, politics. In this and other contexts, this is not a bargain that a modern society will strike. If you make the punishments draconian, people will hesitate to apply them widely. This is true in law enforcement, and it is true of social sins as well. To claim "sexism" too often just robs the word of its power.

So if we want to keep the norm that sexism is very bad, we need to think twice about when we pull out those accusations. Before you shoot, remember that you're not a movie hero with an unlimited supply of ammunition. You're the guy with a single six shooter crouching behind the bar. You have to make every shot count. Aim carefully. When in doubt, hold your fire.

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Megan McArdle is a Bloomberg View columnist who writes on economics, business and public policy.