On Monday, President Trump signed an executive order directing the U.S. trade representative to withdraw America's signature from the Trans-Pacific Partnership, likely delivering a death blow to the controversial multinational trade deal. Opposition to the TPP was a cornerstone of not only Trump's presidential campaign but of Bernie Sanders' also. In a carefully-worded statement, Sanders praised the nation's withdrawal from the TPP without saying a single nice thing about Trump himself.

As preface, it's important to note that Trump's move was almost entirely symbolic. Although the TPP was a favorite project of President Obama, Congress never ratified it, and there wasn't any sign it was going to ratify it anytime soon. The policy was most likely going to die anyway due to Congressional inaction; by signing the executive order, Trump was simply signaling to lawmakers that they shouldn't bother trying to pass the thing they weren't going to pass anyway.

But still, its symbolism shouldn't be overlooked. One of the many ways in which Trump demonstrated early on that he's not your average Republican was by coming out strong against free trade, a reversal of longstanding GOP policy. This put him in the same camp as Sanders, another staunch opponent of TPP and free trade. The two men don't agree on much, but they agree on this.

Shortly after Trump signed the order, Sanders released a statement in support of the move.

The language here is important. Sanders says he is "glad the Trans-Pacific Partnership is dead and gone," talks about how bad free trade is, and says that America needs a new trade policy. He adds that "if President Trump is serious about a new policy to help American workers then I would be delighted to work with him."

What Sanders didn't do is say anything remotely complimentary about Trump. The closest he got to praising the president himself was that last part, but even then, that's not what he was doing. Sanders was speaking purely in hypothetical terms about something (Trump proposing "a new policy to help American workers") that hasn't happened yet.

This was a smart move. One of the biggest threats to the progressive movement in the United States is the possibility of Trump co-opting liberal policies and presenting them as his own, thus consolidating his own support and diminishing the left's in one fell swoop. As the de facto leader of the American progressive left, Sanders' voice holds a lot of influence in the movement. By refusing to give Trump his stamp of approval, Sanders is, for the time being at least, preventing Trump from earning too much credit from the left for his moves on the TPP.

When asked about the development on CNN later in the day, Sanders doubled down on the approach, and spent more time criticizing Trump than applauding him.

The fact that Trump has lefty positions on a few policies — infrastructure, trade, certain areas of foreign policy — presents a challenge and a danger to progressives. If the left wants to succeed as a political movement, it can't allow Trump to subsume its most popular elements during his tenure in the White House. Sanders' refusal to credit Trump on Monday is a good first start in making sure this doesn't happen.