Former Secretary of State John Kerry John Forbes KerryThe Memo: Warning signs flash for Trump on debates Divided country, divided church TV ads favored Biden 2-1 in past month MORE tore into President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE in an interview aired Sunday for the president's latest attacks on former Vice President Joe Biden Joe BidenBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Democratic groups using Bloomberg money to launch M in Spanish language ads in Florida Harris faces pivotal moment with Supreme Court battle MORE, questioning why he is focused on Biden instead of policy issues.

"It's so personal. So unbecoming of a president of the United States to engage in that ... it shows fear or something, I don't know," Kerry said on CBS's "Face the Nation."

"Why is he picking that at this point in time when he has major issues he needs to deal with?" he added.

The former secretary of State was reacting to an interview Trump gave to CBS News last week in which he said Biden would be a "dream" opponent in a 2020 presidential campaign.

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"Look, Joe Biden ran three times," Trump said. "He never got more than 1 percent and President Obama took him out of the garbage heap, and everybody was shocked that he did. I'd love to have it be Biden."

Biden, who has been critical of Trump's policies and rhetoric, is considered among the front-runners for the Democratic presidential nomination in 2020. He has yet to announce if he will run for president.

Kerry lambasted Trump's comments, saying his administration has bungled its response to the president's meeting last week with Russian President Vladimir Putin, and has provided limited information on its ongoing negotiations with North Korea.

"That's what he's trying to run away from. He wants to have you raising the question you just raised with me, which is the real question in the moment, nothing about Joe Biden or what happened in the last campaign and everything," Kerry said.

"What he does is, he's always looking for the diversion, always moving away from the real business of our country because he doesn't know how to do the real business of our country," Kerry said.