President Barack Obama's bid to speedily approve the Trans-Pacific Partnership (TPP), a sweeping free trade agreement linking the United States and 11 other countries on the Pacific, will get another shot on Thursday when the U.S. Senate is set to hold an important test vote.

Just two days earlier, Senate Democrats defied Obama and blocked consideration of a measure that would have allowed TPP to be passed under fast-track rules. Had the measure passed, members of Congress would not have been able to add amendments or filibuster the legislation.

On this second try, enough Democrats are expected to support the legislation after they won scheduling for a separate vote on a bill punishing countries that manipulate their currencies to keep their exports cheap.

The Senate is scheduled to vote Thursday on a customs bill containing the currency rules, as well as an African trade bill that is expected to win strong bipartisan support.

"Though I am of course wary of counting my proverbial chickens before they are hatched ... I expect we will get a strong bipartisan vote in favor of finally beginning debate on these important bills," Senate Finance Committee Chairman Orrin Hatch, R-Utah, said late on Wednesday.

Assuming that Senate Majority Leader Mitch McConnell musters the 60 votes needed in the Senate to limit debate on whether to bring the fast-track trade bill to the floor, senators are expected to spend at least part of next week debating amendments before voting on passage.

Democrats have long been suspicious of trade deals, blaming them for job losses and eroding labor standards. Critics such as Sen. Elizabeth Warren, D-Mass., say that the TPP in particular was negotiated largely in secret, could roll back important financial regulations and would likely give foreign companies ammunition to combat U.S. regulatory policies.

Even if the Senate approves the currency manipulation measure on Thursday, there is no guarantee that the House of Representatives will embrace it. Furthermore, Obama could veto such a bill if it reached his desk, claiming it would threaten free-trade negotiations.

Al Jazeera and wire services