"With regard to Trump, he's saying some things that I just think are ridiculous and would disqualify any other candidate," Johnson told CNN's Chris Cuomo on "New Day."
The former New Mexico governor cited immigration as a particular area of disagreement with Trump, arguing that instead of advocating for a wall and mass deportation, the United States should "embrace immigration." He called building a fence on the border "crazy."
"Speaking as a border governor, they (immigrants) are the cream of the crop," Johnson said.
But when it comes to Sanders, the Vermont senator who trails Hillary Clinton in the Democratic nomination fight but who has ignited legions of young Democratic supporters and independents, Johnson had mostly praise.
"When it comes to economics, we come to a 'T' in the road," Johnson said. "But on the social side of Bernie, I get it."
Johnson said that according to the nonpartisan online political quiz 'iSideWith
,' the candidate he most aligns with is Sanders.
Acknowledging his mutual appeal with Sanders to disaffected, socially liberal voters, Johnson called Sanders' social values "very libertarian."
The libertarian also emphasized his staunch opposition to the "War on Drugs" -- the decades-long effort also denounced by Sanders.
"End the drug war," Johnson said. "The militarization of police, 'Black Lives Matter,' at the heart of all that is the drug war."
The former New Mexico governor also dismissed Clinton -- the likely Democratic nominee -- as the "ultimate technocrat" who would grow the size of government.
"What changes with Hillary Clinton?" Johnson asked. "Government tries to do too much."
The former New Mexico governor faces a crowded field for the Libertarian Party nomination, including cybersecurity legend John McAfee
and activist Austin Petersen.
The Libertarian Party candidate, unlike other third-party candidates, will be the only name alongside the Democratic and Republican nominees on ballots in all 50 states, Johnson said. He added that could be consequential, given the high unfavorability ratings of both Clinton and Trump.
"When you have Hillary and when you have Trump, I think the two most polarizing figures in American politics today, where (are) the 50% of Americans that now declare themselves as independents?" Johnson said.
Whoever the eventual nominee is, the Libertarian Party will face steep odds in the general election. Johnson received
about 1% of the popular vote in 2012, and Bob Barr, the 2008 nominee, received
less than 1% of the popular vote, according to the Federal Election Commission
Turning around the electoral map, Johnson argued, will require a continued presence in polling and an invitation to the general election debates.
"There's no way that a third party wins without being in the presidential debates," Johnson said. "I think the vast majority of Americans are libertarian they just don't know it."