I don't understand why Republican moderates like Boehner and Paul Ryan are pushing so hard for the Trans-Pacific Partnership. What is it they are trying to achieve? I have looked for statements by Ryan on the TPP and have not found any. Why are they supporting it?
The Trans-Pacific Partnership is a proposed (free?) trade agreement heralded by big business.
Both the Democratic and Republican parties and most of their candidates are heavily funded by big business. Arguably the Republican party in particular, but that could be just my impression, I don't have evidence to back it up.
Therefore, Most of them support the Trans-Pacific Partnership. Perhaps quietly so.
If anything, opposition comes from the left. For example, senator Bernie Sanders:
It is incomprehensible to me that the leaders of major corporate interests who stand to gain enormous financial benefits from this agreement are actively involved in the writing of the TPP while, at the same time, the elected officials of this country, representing the American people, have little or no knowledge as to what is in it
Just to be clear, Republicans are not pushing for the TPP yet. The only bill that has gone through congress was one to grant authority to the president to negotiate an agreement and then send it to congress for a simple up/down vote as has been done for many previous trade deals. Allowing congress to amend of filibusterer the agreement could potentially destroy the delicately negotiated agreement between the large number of parties.
Once the final agreement has been negotiated Republicans will have to decide whether or not to support it. At that point we will hear the arguments for and against the specific measures in the TPP
That being said, one of the stated goals of the agreement is to lower tariffs between a large number of nations. Free trade is a core value for many economics minded Republicans. To quote Paul Ryan "We believe in free trade. That is one of our party's primary principles." It's generally seen as enriching American consumers and creating jobs even if there are some losses where America doesn't have comparative advantage. It's at least conceivable that the TPP will lead to freer trade. That being said, if the president does (again) bow to special interests over the interest of consumers, then the house can always vote down the measure.
Since there is plenty of bipartisan cronyism in congress the final TPP will probably have to have some corrupt clauses, but there might be enough legitimate tariff reduction to make it a net good in the eyes of a genuinely free trade Republican like Paul Ryan.