A SEEMINGLY arcane dispute about how to strengthen America’s hand in foreign trade talks—which for 24 hours this week saw Senate Democrats block debate on a negotiating tool sought by Barack Obama—has exposed just how deeply the Democratic Party is divided by global commerce, and whether it is a threat or an opportunity for American workers.

It is rather rare for parties to filibuster their own president. So it was quite a snub when 44 Democratic senators—including about a dozen who normally support his free-trade agenda—voted on May 12th to stall discussion of Trade Promotion Authority (TPA). The stand-off appeared to be resolved a day later when Democratic and Republican leaders in the Senate agreed to look at a raft of trade-related measures before considering TPA. Those measures range from a scheme to compensate American workers hurt by globalisation to a proposal to slap tariffs on foreign rivals accused of making their goods unfairly cheap through currency manipulation.

Mr Obama would probably veto a currency-manipulation bill if one reached his desk—such a law could spark a trade war. But he needs TPA, also known as “fast-track”, to seal foreign trade deals, notably a big agreement under discussion with 11 other Pacific Rim countries, the Trans-Pacific Partnership (TPP), and eventually a pact with the European Union. Under TPA, Congress temporarily gives up its right to amend or unpick trade deals with other governments, retaining only the power to vote yes or no to finished agreements.

In the days before the May 12th rebellion the president angered left-wing Democrats by challenging their populist standard-bearer, Senator Elizabeth Warren of Massachusetts. Ms Warren objects to trade deals being negotiated “in secret”, and is especially suspicious of a dispute-resolution mechanism in recent trade pacts that allows companies to sue foreign governments for enacting discriminatory regulations. She says that this could allow a future Republican president to team up with banks and big business to “override” American financial regulations. Mr Obama says Ms Warren’s arguments “don’t stand the test of fact and scrutiny”.

If anything, TPA faces a rougher ride in the House of Representatives. There Mr Obama’s trade ambitions must run a double gauntlet. To his right lurk perhaps 60 hardline Republicans wary of granting him extra authority on anything. To his left stand as many as 150 House Democrats who either dislike free trade or fear the trade-sceptics who run big unions.

A longer-term philosophical clash lurks beneath this week’s squabbling (loftily dismissed by a White House spokesman as a “procedural snafu”). Mr Obama calls TPP a chance to write global trading rules on America’s terms, which if missed will give China and other rising powers a free hand. But many in his own party take a more defensive view of trade. Representative Sander Levin of Michigan, the leading Democrat on the Ways and Means Committee, says that TPP must include stronger language to make foreign rivals protect workers’ rights and the environment, and avoid currency manipulation, to ensure a “level playing-field” for American workers. “The president says we need to write [global trade] rules, not China. I agree, so let’s write the right rules,” Mr Levin says.

As a result it will take massive Republican support to pass TPA. Hillary Clinton, the putative Democratic presidential nominee, said little during the TPA rebellion, though as Mr Obama’s first secretary of state she said TPP could set a “gold standard” for trade agreements. Her silence is hardly brave, but it does reflect the realities of a divided party.