No one is surprised that 151 liberal Democrats in the House don’t support granting the president fast track authority to negotiate trade agreements. But two groups of Republicans have now signed letters to the President this week joining those Democrats in their opposition. The news media have reported the story as evidence that the tea party opposes President Obama’s trade agenda.

The signatories of the letters are an odd combination of young, party-line Republicans and old-guard isolationists who oppose free trade. Neither group has anything to do with the tea party and both seem confused about how fast track works.

One of the assertions made in the letters is that establishing fast track authority cedes to the President Congress’s constitutional power to regulate trade. This is just wrong. Fast track is not a grant of authority to the President but rather an exercise of authority by Congress.

No one doubts that Congress can pass statutes that regulate trade. Also clear is that the President can enter into treaties with the advice and consent of the Senate. Fast track combines those processes by having the President negotiate the terms of an agreement, after which both houses of Congress pass (or not) a statute that ratifies and implements that agreement.

The contentious aspect of fast track authority comes from the fact that Congress agrees to hold an up-or-down vote on any agreement submitted by the president with no opportunity to add amendments. The good sense of this arrangement is obvious when you consider that a trade agreement is the product of complex and lengthy international negotiations that cannot be adjusted at the last minute just to accommodate each congressman’s pet issue.

But when establishing fast track authority, Congress also imposes restrictions on what must be included (or excluded) from any trade agreement placed on the fast track. In essence, Congress agrees to adopt practical, streamlined parliamentary procedures as long as the President negotiates agreements it likes. Fast track allows Congress to exert influence at an earlier, less-disruptive stage in the process.

While the legitimacy of fast track might be an interesting topic for constitutional scholars, the controversy is mostly a proxy for larger policy arguments about the value of trade in general. Protectionists disapprove of fast track and trade agreements because they want more barriers to trade, regardless of its constitutional status. Similarly, proponents of increased trade approve of fast track because trade agreements put a check on Congress’s tendency to protect domestic industries.

So why have 27 Republicans come out against fast track? Cato’s online trade votes database can help us answer the question.

About half the Republicans who signed the letters are old-guard isolationists who have opposed trade for decades. Indeed, if you were looking for a list of anti-trade Republicans, you need look no further than these signatories. Some of them have been in Congress for over 20 years voting consistently for higher tariffs. You can take a look at the impressive voting records of some these thankfully atypical Republicans here: Rob Bishop, John Duncan, Michael Fitzpatrick, Duncan Hunter, Walter Jones, Frank LoBiondo, David MicKinley, and Chris Smith.

Most of the other Republicans expressing opposition to fast track haven’t been in Congress very long and have voted in lock-step the Republican leadership on trade issues. They have voted in favor of lowering barriers but only in reciprocal trade agreements and they support corporate welfare subsidies like the Export­–Import Bank. I don’t know why they’ve decided to take a stand against fast track, which Republicn leadership strongly favors. Perhaps they really think it’s unconstitutional or perhaps their motives are largely partisan. Significantly adding to the confusion is the fact that of the five freshman who have taken a position against fast track, four of those signed a letter in June emphasizing their support for the policy.

Oddly, there is little doubt that this second group of moderate Republicans will vote in favor of any free trade agreement submitted to Congress even if the President gets “unconstitutional” fast track authority. That’s not at all true of the Democrats who have voiced their opposition—they can be counted on to oppose trade agreements at every step of the way. Ultimately these Republicans seem to be quite confused about what they want and how they should go about getting it. I recommend that they stop listening to their party’s lingering protectionist minority about fast track, or anything else for that matter.