The left’s success in denying President Obama fast-track authority to negotiate the Trans-Pacific Partnership is ugly to behold. The case put forth by a showboating Sen. Elizabeth Warren — that Obama cannot be trusted to make a deal in the interests of American workers — is almost worse than wrong. It is irrelevant.

The Senate Democrats who turned on Obama are playing a 78 rpm record in the age of digital downloads.

Did you hear their ally, AFL-CIO head Richard Trumka, the day after the Senate vote? He denounced TPP for being “patterned after CAFTA and NAFTA.” That’s not so, but never mind.

There’s this skip on the vinyl record that the North American Free Trade Agreement destroyed American manufacturing. To see how wrong that is, simply walk through any Wal-Mart or Target and look for all those “made in Mexico” labels. You won’t find many. But you’ll see “made in China” everywhere.

Many of the jobs that did go to Mexico would have otherwise left for low-wage Asian countries. Even Mexico lost manufacturing work to China.

And what can you say about the close-to-insane obsession with CAFTA? The partners in the 2005 Central American Free Trade Agreement — five mostly impoverished Central American countries plus the Dominican Republic — had a combined economy equal to that of New Haven, Connecticut.

(By the way, less than 10 percent of the AFL-CIO’s membership is now in manufacturing.)

It’s undeniable that American manufacturing workers have suffered terrible job losses. We could never compete with pennies-an-hour wages. Those low-skilled jobs are not coming back. But we have other things to sell in the global marketplace.

In Washington state, for example, exports of everything from apples to airplanes have soared 40 percent over four years, to total nearly $91 billion in 2014, according to The Seattle Times. About 2 in 5 jobs there are now tied to trade.

Small wonder that Sen. Ron Wyden, a liberal Democrat from neighboring Oregon, has strongly supported fast-track authority.

Some liberals oddly complain that American efforts to strengthen intellectual property laws in trade deals protect the profits of U.S. entertainment and tech companies. What’s wrong with that? Should the fruits of America’s creativity (that’s labor, too) be open to plundering and piracy?

One of TPP’s main goals is to help the higher-wage partners compete with China. (The 12 countries taking part include the likes of Japan, Australia, Canada, Chile, Mexico and New Zealand.) In any case, Congress would get to vote the finished product up or down, so it isn’t as if the public wouldn’t get a say.

But then we have Warren stating with a straight face that handing negotiating authority to Obama would “give Republicans the very tool they need to dismantle Dodd-Frank.”

Huh? Obama swatted down the remark as wild, hypothetical speculation, noting he engaged in a “massive” fight with Wall Street to get the reforms passed. “And then I sign a provision that would unravel it?” he told political writer Matt Bai.

“This is not a partisan issue,” Warren insisted. Yes, in a twisted way, the hard left’s fixation over big corporations has joined the right’s determination to undermine Obama at every pass.

Trade agreements have a thousand moving parts. The U.S. can’t negotiate with the other countries if various domestic interests are pouncing on the details. That’s why every president has been given fast-track authority over the past 80 years or so.

Except Obama.

It sure is difficult to be an intelligent leader in this country.

Froma Harrop is a syndicated columnist. Follow her on Twitter @FromaHarrop. She can be reached by email at: fharrop@gmail.com.