Cross over votes and some name recognition.
Now I would note it looks like all of the democratic Senate candidates are receiving less cross over votes then the last time their seats were up in a presidential election year (2012). They also seem to be doing worse then relative to the Congressional ballot in 2018.
I would note that with the exception of ME senate 2020- the number of cross over support in polls FOR Senate elections has declined as the election has gotten closer. See ND, TN, MO 2018. GA regular 2020, etc.