KEY POINTS
  • "When Trump goes after the Mexican government, which has already made a bunch of concessions in the NAFTA renegotiations, it makes investors nervous [and] makes them want to sell," Jim Cramer says.
  • "It feels like there's no plan, like anything could happen, and that's a bad feeling because the markets hate uncertainty," he says. 
  • "In an era where all that matters is who's next for punishment, we need to be very cautious," the "Mad Money" host says.

CNBC's Jim Cramer on Friday drew a line in the sand on President Donald Trump's attempt to negotiate trade via Twitter.

After supporting a hard-line trade stance against China, Cramer denounced the surprise 5% tariffs that Trump has threatened to slap on all imports from Mexico starting next month. The threat sent the three major U.S. indexes down between more than 1% each Friday.