There couldn't have been a more pivotal moment in the U.S.-Mexican relationship for the Philadelphia Museum of Art to open a landmark exhibit of Mexican art.

Of course, the timing of this stunning show is coincidental, coming in the midst of a presidential campaign in which Donald Trump has labeled illegal Mexican immigrants as criminals and rapists. He has also repeatedly denounced the NAFTA trade accord with Mexico.

Yet it is impossible to separate this brilliant show - "Paint the Revolution: Mexican Modernism 1910-1950" - from politics. These masterpieces by Diego Rivera and other greats were painted at a time when Mexicans were furiously debating their political direction; they arrive here while America is going through unprecedented political turmoil. Mexican immigrants and the U.S.-Mexico relationship have been used by Trump as a piñata that he constantly whacks to woo his faithful.

Last week, I had a chance to discuss all this with Mexico's elegant foreign minister, Claudia Ruiz Massieu, who was in Philly for the exhibit's opening and who has made 30 trips this year to the United States. She hopes to set the record straight.

"We see the need to inform the American people better about the strategic value and many benefits of our relationship," she told me. "The best way to meet prejudices is to talk objectively about the contributions of our community to the United States."

Of Trump's broad-brush portrayal of migrants as criminals, she says, "The picture Trump has presented is misinformed and prejudiced." It ignores the fact that most illegals work and a large percentage pay taxes (and it also insults the many successful Mexican American businessmen and professionals). Moreover, Trump never tells you that Mexico has a negative rate of migrant inflow into the United States.

As documented by the Pew Research Center, since 2009 more Mexicans have returned to Mexico than have migrated here (most now illegally crossing the border come from Central or South America or the Caribbean). One reason for the falling numbers is that - surprise! - border security and deportations have increased in recent years.

However, Massieu is quick to say that the problem of undocumented immigrants needs addressing by both countries. "We have to work together to meet the challenge of migration flows," Massieu says. "We also need to work on root causes of migration in countries of origin."

Trump's talk of lining the border with a concrete wall - debunked by most experts as geographically impossible and prohibitively costly - doesn't fly with Mexico.

Will Mexico pay for the wall, as Trump insists? "We wouldn't even consider it," Massieu swiftly responds. "This is an absurd proposition."

Why then did Mexican President Enrique Peña Nieto invite Trump to visit and never publicly repudiate the "Wall" proposal in his presence?

Massieu's explanation: "Our government believes in dialogue, particularly when there is a candidate who has a glaring lack of knowledge of what our country contributes to U.S. growth."

Which brings us to the subject of NAFTA, a trade accord with Mexico and Canada that was passed on President Bill Clinton's watch. Trump calls it "one of the worst deals ever" and says he'd renegotiate or junk it because it has sucked out American jobs. He pledges to "bring our jobs back."

What Trump doesn't say is that many of those manufacturing jobs - so prevalent in the 1960s and 1970s - have been overtaken by automation and are never coming back. Moreover, Mexico, the United States, and Canada are now tied into a single integrated economy that would be extremely difficult to tear apart.

"For every dollar spent on Mexican exports, 40 percent is U.S. content," Massieu says. In other words, the less complex parts of an American car may be made in Mexico, the more complex parts in the U.S., and the car assembled there, or here.

"Technically it is possible, [to disrupt that chain] but in reality it is not possible to undo the commercial chains and production ties we have," Massieu says, especially because those chains extend beyond governments and link industries in many states directly to Mexico, including Pennsylvania.

If Trump tore up NAFTA and imposed tariffs on Mexico, it would destroy many jobs north of the border without the certainty of creating new ones. American consumers would have to pay far more for their goods.

None of this is to say that there are not problems with immigration or some provisions of trade deals. Pressed from the left by Bernie Sanders, Clinton has echoed Trump in rejecting the trade deal that was supposed to supersede NAFTA, the Trans-Pacific Partnership. Mexico is waiting uncertainly to see what she would do, if elected, on trade.

But there is no question whom the Mexicans would prefer to win the U.S. election. "Candidate Trump doesn't have the knowledge of our bilateral relationship that Mrs. Clinton has," says Massieu. "She knows the strategic value of our relationship."

"We will work with whatever government, no matter who wins," the minister adds. But the U.S.-Mexican relationship would no doubt turn frosty under a President Trump.