Fact check: Trump-tweeted ad unfairly blames Democrats

President Trump tweeted an ad that blames Democrats for allowing a Mexican man who was in the U.S. illegally to kill two police officers in Northern California in 2014 in methamphetamine-fueled attacks. Luis Bracamontes was sentenced to death.

The ad shows video of Bracamontes saying in court that he wished he had killed more police officers, one of his many outbursts before the judge.

The ad links Bracamontes' crimes to a large caravan of Central American migrants moving through Mexico and suggests that Democrats will allow other criminals in the U.S.

A look at claims in the ad:

Ad: "Democrats let (Bracamontes) into our country."

The facts: That's like blaming Republicans for criminals who entered the country illegally under Trump or President George W. Bush.

Bracamontes, who is from the Mexican state of Sinaloa, came to the U.S. illegally in June 1996, during Democrat Bill Clinton's administration. He was arrested three months later on drug charges after purchasing crack cocaine from an undercover officer at a Phoenix apartment and deported in 1997 after completing his sentence.

He was arrested for marijuana possession in Arizona in March 2001, during the Bush administration. It's unclear when he returned to the U.S. illegally before that arrest.

Ad: "Democrats let him stay."

The facts: Bracamontes was deported four times before he killed Sacramento County sheriff's Deputy Danny Oliver and Placer County sheriff's Detective Michael Davis Jr., according to Sacramento County Sheriff Scott Jones.

There is no evidence that any Democrat — or anyone, for that matter — allowed Bracamontes to stay.

Democratic and Republican administrations alike have deported hundreds of thousands of people a year. Barack Obama focused during his second term on recent arrivals and people with criminal histories, but Trump quickly directed that anyone in the country illegally could be targeted.

Ad: "Who else would Democrats let in?

The facts: The ad mixes footage of Bracamontes with what appears to be a large caravan and a Fox News interview with a migrant in the caravan who acknowledges a conviction for attempted murder.

Trump has said migrants in the caravan include criminals without offering any evidence, part of a pattern of linking immigrants in the country illegally to crime.

Some studies have found immigrants are less likely to commit crimes than people born in the United States.

Ruben Rumbaut, a University of California, Irvine sociology professor, co-authored a recent study that noted crime rates fell sharply from 1990 to 2015 at a time when illegal immigration spiked. Crime rates were low in immigrant rich cities and among lowest along the border, like El Paso, Texas, and San Diego.

Alex Nowrasteh of the libertarian Cato Institute, reviewed academic literature in 2015 and found, "With few exceptions, immigrants are less crime prone than natives or have no effect on crime rates ... (The) research is fairly one-sided."