MN is not NJ
Maybe it's just cause I live in NJ, but I see a huge difference between replacing a candidate who gets killed in a plane crash right before an election in a state where the law clearly states that it's OK to do so, and putting up a candidate that you know is dirty then dumping him 5 weeks before the elsection when the polls show he's getting his ass kicked by an unknown newcomer, and the law says it's OK to do that 7 weeks before.
As a practical matter, Mondale and Lautenberg are no-brainers. The only thing the dems have time for in either race is a well-known name.
That gives us the next difference. Mondale reportedly has no plan to campaign, just be available, which could be enough.
Lautenberg is campaigning but seems to be afraid to debate Forrester. To my mind, that's a dirty campaign. And yes, it's dirty in NY too when the candidate ducking debate is a republican.