When RN mistakenly declared Charles Manson guilty during his trial, problems ensued.  From a contemporaneous report in Time:

In Los Angeles, the effect of Nixon’s remarks on the Manson trial was instant and dramatic. While the Los Angeles Times came out the same afternoon with a four-inch headline reading MANSON GUILTY, NIXON DECLARES, Judge Charles Older went to great lengths to ensure that the jury, which has been sequestered since the trial began, would not learn of Nixon’s remarks. The windows of the jury bus were whited over with Bon Ami so that no juror could glimpse the headline on street newsstands. If the jury discovered Nixon’s verdict, the defense might have grounds for a mistrial. His efforts were to no avail. Next day Manson himself displayed a copy of the Times to the jury for some ten seconds before a bailiff grabbed the newspaper from his hands. Judge Older called a recess, then questioned the jurors one by one to satisfy himself that their judgment would not be affected. An alternate juror convulsed the courtroom when he announced his disclaimer: “I didn’t vote for Nixon in the first place.”
As noted in a previous post, President Obama committed a similar error when he prematurely pronounced sentence in the KSM case: “I don’t think it will be offensive at all when he’s convicted and when the death penalty is applied to him.”  Yes, Obama quickly modified his remarks, but so did RN.  Arguably, Obama’s blunder is much worse.  First, it took place before jury selection, so it would be impossible to prevent potential jurors from knowing about it.  Second, a defense attorney could easily argue that Obama’s words carry great weight in Manhattan, where the trial will take place.  In 2008, the  borough gave him 85.7 percent of its vote.