What's clear about the Donald Trump-Mexico deal on migrants and tariffs? It's unclear.

President Donald Trump has no cohesive strategy for dealing with either trade or immigration. He falls back on a default position of drawing attention to himself by threatening to create a crisis and then taking credit for defusing it.

The latest example of this is the saga of Trump, Mexico, migrants and tariffs.

For those who haven’t followed its zigzagging details, the episode started with an irate Trump threatening steep tariffs on imports from Mexico to pressure it to do more in stopping the flow of caravans from Central America.

It moved on to American businesses warning of the grave economic consequences of the proposed tariffs, and ended with Trump striking a deal of marginal significance and trying to obscure his retreat with a fusillade of tweets.

In those tweets, he initially declared victory, then lashed out at news organizations once they began picking the deal with Mexico apart and concluded that that there was less to it than meets the eye.

More:President Trump's tariff strategy produces a game-changing win

If the usual carping at the media weren’t enough, the president claimed, in all caps with no supporting evidence, that “MEXICO HAS AGREED TO IMMEDIATELY BEGIN BUYING LARGE QUANTITIES OF AGRICULTURAL PRODUCT FROM OUR GREAT PATRIOT FARMERS!”

Several days after Trump's victory declaration, much remains murky.

Is there a secret immigration deal, as Trump asserts, or merely an understanding to review progress after 45 days, as Mexican officials suggest? Has Mexico actually agreed to buy any more U.S. farm products? Does Mexico have thousands of national guard troops available to deploy to its southern border, and when might they get there? And how does this whole kerfuffle affect the proposed replacement for the North American Free Trade Agreement?

What is clear is that Trump’s threatened tariffs are a crude tool — and his ongoing messaging on immigration isn't likely to stem the tide of people fleeing violent, gang-dominated nations like Honduras, El Salvador and Guatemala.

If anything, the rhetoric might be encouraging it. People in those countries are constantly being reminded by Trump of the migrants making the trip north. And they may think that things will get worse so they should leave now.

Any effort to deal with the flow of asylum-seekers has to start with a realistic set of goals and a comprehensive plan for how those goals will be realized. Realistic in this case means not trying to eliminate all migration instantly and not alienating Mexican leaders, whose cooperation is needed to stem the caravans of both Central Americans and deadly cartel-produced drugs into the United States.

One key in dealing with the Central American influx is to process most applications for asylum in Mexico, rather than at the U.S. border. Mexico has, in fact, already agreed to consider this.

Another is to look at the signals sent to would-be immigrants. A 2008 U.S. trafficking law, for instance, creates a separate set of immigration standards for Canada and Mexico and is widely viewed in Central America as an open invitation to people from other countries.

The best approach is to get Congress to change that law, and to help Central American governments reassert control and bring about safer, more stable conditions.

This has a chance to work, though not overnight. What won’t succeed is more Trump tweets, tariffs, tantrums and theatrics.

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