Howard Schultz (Getty Images)

US president Donald Trump took to Twitter to slam former Starbucks CEO Howard Schultz on Monday morning, following Schultz's announcement of a possible presidential run.

"Howard Schultz doesn't have the 'guts' to run for President!" Trump tweeted. "Watched him on @60Minutes last night and I agree with him that he is not the 'smartest person.'"

The tweet continues: "Besides, America already has that! I only hope that Starbucks is still paying me their rent in Trump Tower!"

On Sunday, Schultz said in an interview with "60 Minutes" that he is "seriously considering running for president as a centrist independent."

Schultz left Starbucks in 2018 after more than three decades leading the coffee giant.

In Sunday's "60 Minutes" interview, Schultz repeatedly criticized Trump for his lack of qualifications. Schultz said he would run as an independent due to shortcomings of both Democrats and Republicans.

"Not only the fact that this president is not qualified to be the president, but the fact that both parties are consistently not doing what's necessary on behalf of the American people and are engaged, every single day, in revenge politics," Schultz said.

Correspondent Scott Pelley also noted that Schultz is wealthier than Trump, according to a Forbes report that estimated his net worth to be $3.4 billion (R47 billion). Schultz responded that his campaign would be "fully resourced," due to his immense wealth, and that he would be willing to release his tax returns immediately.

Pelley also brought up the likelihood that Trump would respond to Schultz's run on Twitter.

"I've become bored with President Trump and his tweets," Schultz responded.

Schultz's criticism of Trump began before the former Starbucks CEO parted ways with the company.

In September 2016, Schultz endorsed Hillary Clinton for president - his first time publicly endorsing a candidate.

That December, he announced plans to step down as CEO, saying he would instead be focusing on Starbucks' "social missions" as chairman. In January 2017, he blasted Trump's attempt to bar refugees from entering the US, inspiring boycott threats from the right. In August 2017, he wrote a piece in the Financial Times about national identity after white supremacists rallied in Charlottesville.

Despite Schultz's criticism, there is a Starbucks open in New York's Trump Tower. In 2015, Trump said that it was a very successful location, while calling for a boycott of Starbucks because the chain did not say "Merry Christmas."

Receive a single WhatsApp every morning with all our latest news: click here.

Also from Business Insider South Africa: