The House Republican border adjustment proposal to tax imports is “insane,” media mogul Steve Forbes said on Wednesday.

“The Republicans are proposing this crazy tax. They’re going to punish American consumers over $100 billion a year” over 10 years by making goods coming into the US more expensive, CNBC quoted Forbes — a two-time GOP presidential candidate — as saying.

The people who would be hurt most by the border tax would be middle-class workers who elected Donald Trump as president, Forbes said.

“Economically it’s wrong. Politically it’s wrong,” he said, adding that the efforts by Republicans to reduce taxes should not include a new tax.

The chairman and editor-in-chief of Forbes Media unsuccessfully sought the GOP presidential nomination in 1996 and 2000. He ran on a platform for a flat tax to apply consistent rates across all brackets.

Just implement a “straight vanilla tax cut. We’ve done that before. It works,” Forbes said.

He also warned that if Trump and Congress “botch” the tax cuts, the Grand old Party could lose its majority in the House in the 2018 midterm election.