They see themselves as the rebels, fighting those in power. You're not going to get much going down that road.
I suspect in Harris' case it has more to do with trying to distance herself from the Biden administration as much as possible to save her own career. Being put in charge of the border looks to me like where the schism between the two of them really began, because in a lot of ways it's setting her up to fail:
-Huge surge to the border the second the administration is sworn in because every Democrat was pandering hardcore for Open Borders during the election
-Can't conduct mass deportations without incurring massive backlash from media and the party base
-Can't do actual open borders without the southwest
hard flipping back to Republicans (this is already being seen in border counties in TX)
-Margin of victory in Congress is far too narrow to overcome bipartisan deadlock on immigration reform/amnesty
-Best option is to compromise and try to keep media attention away from the border surge while quietly shipping immigrants to states further inland away from prying eyes, plus you can flip more of the heartland that way
-Federal court gets wise to what you're doing and smacks that down, insisting you return to the "Remain in Mexico" policy of sorting out refugee applications
-Then Haiti goes horribly to shit and a new, even bigger migrant surge hits the border immediately afterwards.
She's got no good options, she was publicly put in charge, and figuring out a way to put the onus on the dementia patient's irresponsibility is the only way to try and salvage any future political prospects.