It is not even about free-trade. The actual reason is that it's about Colombia. Venezuela would fit to them better.

>Changing the rules after the fact seems to be a trend with this bunch. However, this time it is not simply affecting a house vote's timing or the Democratic primary, this time they're damaging the ability of the President (office not current occupant) to engage in good-faith treaty negotiations.
>
>"The Democratic Party's protectionist make-over was completed yesterday, when Nancy Pelosi decided to kill the Colombia free trade agreement. Her objections had nothing to do with the evidence and everything to do with politics, but this was an act of particular bad faith. It will damage the economic and security interests of the U.S. while trashing our best ally in Latin America."
>http://online.wsj.com/article/SB120778566399303309.html