(CNN) President Donald Trump's Twitter declaration that the man charged with killing eight pedestrians and bikers in New York City "SHOULD GET THE DEATH PENALTY" has ignited controversy over whether Trump could have jeopardized the government's legal case.

Presidents have uttered vengeful statements in the wake of terror attacks and terrible murders before. Yet, as with all things Trump, his late-night missive went further and could cause greater trouble for prosecutors.

Still, with history as a guide and the present context of a defendant who apparently mowed down people in the name of ISIS, it is likely Trump's intemperate tweet has complicated -- but not wrecked -- the prosecution's ability to obtain the ultimate penalty.

Judges bring extra scrutiny to capital cases, and federal prosecutors must show they are seeking the death penalty based on fair-minded, well-considered grounds distinct to an individual defendant. The rapid-fire (some might say knee-jerk) nature of a Twitter message by the person at the helm of the executive branch that includes the Justice Department, could undermine that deliberative process.

"It is entirely inappropriate for the President to call for a specific punishment for a federal criminal defendant, especially one who has not been convicted," said Ron Weich, dean of the University of Baltimore law school and a former federal prosecutor.

Read More