Do you really believe Harris is going to be the Democrat's likely nominee? I know that polls one year before the primaries are meaningless (Jeb was at the top of the GOP polls in early 2015), but even ignoring the low poll numbers, she doesn't have either the name recognition or the Democrats' political machine throwing their weight behind her that's necessary to win.
My guess is Buttgig is using the publicity of his Presidential campaign to get a Congressional seat or something along those lines.
I think she actually does have the Obama machine behind her. Early polls like this tend to pretty much reflect name recognition.
Buttegieg (sp?) appears to be the CIA candidate and is pretty clearly the brightest of the bunch, but I think he’ll end up tucked under Harris.
Of course, there’s a long, long ways to go. Even the year that McCain got it, he was nowhere in the polls for months. Similarly, Kerry.