Donald Trump fires back at 2016 rival: You 'couldn't be elected dog catcher'

Real-estate magnate Donald Trump fired off angry tweets at one of his GOP rivals in the presidential race Wednesday, accusing him of being a has-been who couldn't get elected to office again.

The rival, former New York Gov. George Pataki (R), has recently been criticizing Trump's controversial comments about illegal immigration.

Pataki told Business Insider on Tuesday that Trump was "disrespectful" and subsequently wrote a letter to the Republican field urging them to join him in denouncing Trump. 

Trump, as is his wont, responded by trashing Pataki on Twitter:

Trump is being heavily criticized by businesses, celebrities, and others after he used harsh rhetoric to describe Mexican migrants during his campaign launch last month. Among other things, Trump accused Mexico of sending its "rapists" and drug runners to the US.

"When Mexico sends its people, they're not sending their best; they're not sending you," Trump said then, according to a transcript. "They're sending people that have lots of problems, and they're bringing those problems with us. They're bringing drugs. They're bringing crime. They're rapists. And some, I assume, are good people."

Earlier in the day Wednesday, Macy's said it was snubbing Trump because of the "disparaging characterizations" he made during his campaign launch. NBC, Univision, and the Mexican media company Televisa all similarly announced they would not show Trump's Miss Universe Organization beauty pageants.

For his part, Pataki told his fellow Republicans rivals that condemning Trump's remarks would represent true leadership on their part.

"As Donald Trump doubles down, I'm asking you to join me in standing up.  Stand up for our party, for the ideals that made America great, and stand for the basic decency and integrity entitled to every American, no matter their heritage or nationality," Pataki wrote in the letter. "Join me. Stand up now. Denounce his comments today."