Bernie and Trump are the only candidates currently running who were against the war in Iraq in 2003 (a view that was considered naive and "far left" at the time, even by the editor of this paper, http://www.thestranger.com/seattle/say-y…
, although a view that makes a lot of sense given the significant loss of life and money from the war). Bernie, Trump, and Rand Paul share a non-interventionist approach to foreign policy and Trump is arguably the second most liberal politician in either party who shares that view.
On economic issues, Trump is arguably the most moderate Republican in the race, though to the right of both Sanders and Clinton. Trump is also one of the few Republican candidates who actually wants to preserve access to affordable healthcare, safeguard social security and other social programs, and invest in women's healthcare (not that he has much competition in that party).
Although Trump's far right stance on immigration may cost him some Bernie voters, others may look past it with the recognition that the stance would likely be DOA. Any Trump immigration plan would have to pass both houses of congress, a filibuster in the Senate, and a Supreme Court ruling, something that is highly unlikely without substantial moderation and buy in from Democrats.
If either the Democratic or Republican primary is locked up by Super Tuesday, anti-interventionist independents and moderates from one party could potentially take a closer look at the most moderate, anti-interventionist option in the other party, even if he has a loud mouth, a New York accent, and weird hair.