Sen. Cory Gardner (R-Colo.) on Capitol Hill on March 20, 2017. (Alex Wong/Getty Images)
Opinion writer

Sen. Cory Gardner of Colorado is arguably the most vulnerable Republican fighting for reelection to the upper chamber in 2020. As FiveThirtyEight noted recently, Colorado is blue-leaning; Gardner won reelection by a very tight margin in 2014; and multiple Democrats are lining up to take him on, a key signal of weakness.

So it’s a key tell that Gardner is putting himself firmly on record against Trump’s threatened tariffs on Mexican goods, even before they take hold:

GOP Sen. Cory Gardner is raising the alarm about Donald Trump’s tariff threat just three days before the president’s proposed penalties against Mexican imports take effect.

The Colorado Republican distributed a letter to his Republican colleagues on Friday afternoon warning “current and proposed tariffs would negate all the economic benefits of tax reform” as Trump prepares to slap a new 5 percent tariff on Mexican goods that could increase to as much as 25 percent.

The president has said those levies would go into effect on Monday without border reforms from Mexico aimed at stopping illegal immigration to the United States.

Facing a tough reelection campaign in a blue state next year, Gardner said that the new tariffs would take money from workers and that “hardworking Americans are unlikely to overlook the hit to their pocket books.”

It’s notable that Gardner is citing that new study from the Tax Foundation — which your humble blogger wrote about earlier this week — finding that Trump’s tariff wars could end up negating whatever meager gains ordinary Americans got from the Great and Glorious Tax Cut of 2017.

In so doing, Gardner is openly conceding that Trump’s tariffs are harming Americans economically and threatening to undo Trump’s tax cuts, which were supposed to be all about benefiting the middle class (but actually lavished a great percentage of benefits on top earners). That’s going a good deal further than objecting on strictly ideological grounds, an easier position for Republicans to take, since it does not point out tariffs’ negative practical impact on voters.

Along those lines, this line from Gardner’s letter is also notable:

I am all for fair trade. I am all for securing our border. But I am not for turning our backs on American workers and consumers. Nor can I turn my back on the free market truths that have made America’s economy the strongest in the world.

Wait, what? Trump’s tariffs constitute “turning our backs on American workers”?

How often have you heard Republicans make that concession? After all, it directly undercuts Trump’s entire message about his trade wars.

That message is twofold: first, that Trump’s trade wars, particularly with China, have been conducted for the broad goal of forcing fairer trade deals on behalf of U.S. workers; and second, that the tariffs themselves are being taken from the target countries, also to the benefit of U.S. workers.

That latter claim is nonsense, of course — tariffs are not paid by the target countries; they are costs passed on to U.S. consumers. But, with the trade wars dragging on and on, creating disruptions that are harming Trump’s own constituencies, Trump has been forced to make this claim, to create the impression that even while they are taking a hit, he is taking back money those countries took from us.

In the case of China, that has led Trump to develop a convoluted narrative to the effect that this tariff money is being taken from China and delivered back to farmers through the purchase of their products to deliver to other countries that need them.

Trump has hatched a similar tale about the threatened Mexico tariffs. The difference here is that those aren’t really about trade; they’re about forcing Mexico to do more to stop migrations from Central America.

To be clear, Trump could actually end up winning real concessions from Mexico on that front, preventing the tariffs from going into effect, though how much of a dent that would make in the broader asylum crush — and, more to the point, what that would mean in humanitarian terms for migrants — remains unclear.

But Trump has laid the groundwork for the tariffs to go into action, and here’s the story he’s created in case that happens:

Or, as Trump put it elsewhere: “The higher the Tariffs go, the higher the number of companies that will move back to the USA!”

Never mind those studies showing that the totality of the tariffs could wipe out the tax cut’s meager gains. Never mind that economists are warning that if the Mexican tariffs go forward, it could tip us into recession.

The story now is that if the tariffs do go forward, that’ll be good for America, because it will bring lots of jobs back to the United States!

In that context, having a Republican senator concede that the tariffs are actually bad for ordinary Americans’ finances — and even bad for American workers — seems like quite an admission.

Read more:

Greg Sargent: Trump’s worldview is failing spectacularly. Several new studies illustrate how.

Robert J. Samuelson: There is a sheer nastiness to Trump’s Mexico tariffs

Catherine Rampell: Just a few of the reasons that Trump’s Mexico tariffs are deeply stupid

Greg Sargent: Trump is staking reelection on one of his biggest lies

George F. Will: The vast incoherence of President Tariff Man