(CNN) Former Homeland Security secretary Jeh Johnson has come out against Democrats' calls to abolish the Immigration and Customs Enforcement agency, slamming it as an unserious policy proposal that could jeopardize immigration reform.

"The reality is that abolishing ICE is not a serious policy proposal; it's about as serious as the claim that Mexico's 'gonna pay for the wall,'" Johnson wrote in a Washington Post op-ed published Friday, referring to President Donald Trump's campaign promise that Mexico would fund the building of a massive wall on the southern border.

The former head of the Department of Homeland Security under President Barack Obama said that the calls to abolish ICE "only serve to sow even greater division in the American public and in its political leadership, damaging any remaining prospect of bipartisan immigration reform."

Johnson also argued that eliminating the immigration enforcement agency, which also investigates drug smuggling and human trafficking across borders, would compromise public safety.

"If Americans don't like ICE's current enforcement polices, the public should demand a change in those policies, or a change in the leaders who promulgate those policies," Johnson wrote.

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