Donald Trump's voters may love his outspoken ways. But judges? Not so much.

The president's tweets already have played a role in court decisions blocking his bans on travel and transgender members of the military.

The judge deciding Sergeant Bowe Bergdahl's sentence also has said he might take Trump's scathing criticism of Bergdahl into account. And now the president is calling for the death penalty for the suspect in the bike path attack in New York.

Lawyers for the suspect in the New York attack, Sayfullo Saipov, almost certainly will argue that Trump's two tweets saying Saipov should get the "DEATH PENALTY" will make it harder for their client to receive a fair trial or sentence.

Although some legal experts said judges in Manhattan's federal courts will not let the president's remarks throw the case off track, Trump's comments broke with longstanding tradition against presidents publicly commenting on criminal cases.

"Once again, the president sabotages his own lawyers, and makes it virtually impossible to provide the defendant with a fair trial," South Texas College of Law professor Josh Blackman said on Twitter.

Trump's first comment came around midnight, a few hours after prosecutors filed federal terrorism charges against Saipov, a 29-year-old immigrant from Uzbekistan.

Authorities say Saipov was inspired by the militant Islamic State group when he veered into a city bike path in Manhattan on Tuesday, killing eight people.

The court filing signaled an intent to prosecute him in civilian courts in the United States and was at odds with earlier comments by Trump and others that he might be held as an "enemy combatant" or even be sent to the naval brig at Guantanamo Bay, Cuba.

By Thursday morning, Trump himself said Saipov would be prosecuted in New York, which the president said would be faster than subjecting him to a military tribunal at Guantanamo.

No one held in the US has been sent to Guantanamo since the detention center opened in January 2002.

"There is also something appropriate about keeping him in the home of the horrible crime he committed. Should move fast. DEATH PENALTY!" the president said in a tweet.

The Obama administration made a similar argument in trying to move the five men accused in the Sept 11 attacks from Guantanamo to New York for trial in a civilian court, an effort that was derailed by political opposition.

The men remain at Guantanamo and have yet to be tried. Their cases are likely years from resolution.

The president's potential for influencing a criminal case also has arisen in the court martial of Bergdahl.

The Army sergeant's lawyers said candidate Trump's description of Bergdahl as a "dirty rotten traitor" who should be executed unfairly affected his trial.

Bergdahl faces up to life in prison after pleading guilty to charges that he endangered comrades by walking off his post in Afghanistan in 2009.

The judge, Army Colonel Jeffery Nance, has said he was not directly affected by Trump's criticism of Bergdahl, but that he would consider Trump's comments as a mitigating factor in the sentencing.

Trump is not the first president to comment on the guilt and appropriate punishment of someone facing trial in notorious killings.

Richard Nixon weighed in on Charles Manson's guilt and Barack Obama suggested execution was the right sentence for accused Sept 11 mastermind Khalid Sheikh Mohammed, though both presidents walked back their comments in short order.

But the advent of social media has allowed Trump to comment on a wide range of topics at any hour of the day and without any filter.

And he has persisted in his use of Twitter, in particular, even after his allies have suggested some tweets are counterproductive.

Past presidents have kept diaries with their uncensored views of events and people, but they also have kept those entries private until long after they left the White House, presidential historian Douglas Brinkley said.

"Trump's kind of a diarist in real time, and there's nothing comparable," said Brinkley, a history professor at Rice University in Houston.

Beyond criminal cases, some judges are taking account of Trump's tweets and other seemingly unscripted remarks to assess the motivations behind policies, including a ban on visitors to the United States from several mostly Muslim countries and a ban on transgender members of the military.

The latter was actually announced in a series of tweets beginning at 5:55 am on July 26.

US District Judge Colleen Kollar-Kotelly incorporated screen grabs of the tweets into her 76-opinion that blocked the transgender service member ban and cited "the unusual circumstances surrounding the President's announcement" among her reasons for doing so.

In the travel ban cases, Trump's tweets both as a candidate and president were invoked by several judges who blocked the ban from taking effect.

Judges, like everyone else, can't ignore what the president is saying.

“The president's habit of sharing his running commentary with the country inevitably influences how his, and his administration's, actions are understood and interpreted, by courts and citizens alike,” said Richard Garnett, a University of Notre Dame law professor.

But Garnett also cautioned that judges should be hesitant to rely too heavily on Trump's tweets in assessing whether policies are legal.

"You don't want to have a judicial doctrine where you're going to slap down policies kind of like you ground your teenager as punishment for what we regard as reckless tweets. That can't be the basis for deciding whether something is constitutionally authorised," he said.