From a S.F. Chronicle op-ed today:
The opposition to Kavanaugh is actually not about him, but about the man who nominated him, Donald Trump. Democratic senators — especially those running for president or for re-election in liberal states — want to show their political base that they are part of the resistance to everything Trump stands for. The irony is that Kavanaugh is a remarkably un-Trumpian nominee.
Whereas Trump is populist, intentionally divisive, anti-establishment, immoderate, and contemptuous of many of traditional norms of comity and civility, Kavanaugh is a product of the establishment, gets along with colleagues across the spectrum, respects precedent and plays by the rules. Any Republican president would have placed Kavanaugh on his short list. He has no associations with the Trump wing of the Republican Party. Trump nominated him in deference to the legal elite of the party, including the Federalist Society, many of whom are as concerned about Trump's character and disposition as any Democrat.
The notion that any Trump nominee is illegitimate because he would shield Trump from hypothetical future subpoenas or prosecutions is belied by history. Nixon's appointments voted against him in United States vs. Nixon, and Clinton's appointments voted against him in Clinton vs. Jones. Kavanaugh has no closer relationship to Trump that those appointees did to the presidents who appointed them.
This strikes me as quite right; you can read the whole op-ed here.