Maybe Democrats should consider this scenario: Hillary wins, but Republicans control the Senate. You think McConnell lets Garland through knowing that he'll suffer zero electoral consequences if he doesn't? Hell no. Hillary would be a lame duck likely to inflict extreme downballot damage in the party in the midterms. With Trump, Democrats also have a chance of getting family leave through and at making significant inroads downballot, where there would've been a zero chance under President Hillary. And with President Hillary, they'd have been screwed for redistricting and thus out of the House for another decade. So, is the chance that you MIGHT get Garland really worth it? It's not like Trump has been able to do anything that significant anyway.
Yeah, Republicans were already planning on blocking any nominee from a very unpopular President Hillary Clinton.
https://www.theatlantic.com/politics/archive/2016/11/whats-the-opposite-of-court-packing/506081/
And there's a good chance Hillary never would've gotten the chance to replace Breyer and Ginsburg before 2020. What, especially with an increased R Senate majority after 2018. In that scenario, I think it's likely that they would be replaced by whichever R would've won in 2020 (I stand by both Hillary and Trump being one-term presidents under about any scenario).
If Clinton won PA, she probably pulled McGinty across the line with her, but that's still a GOP majority unless Kander also gets swept in. Even then, the Dem majority through VP Kaine could be gone as soon as Nov. 2017 with the special in VA. Beyond McGinty and Kander, there almost surely wouldn't be any more Dem pickups if the presidential race was still close.
Garland almost surely would get through even with a 51-53 seat GOP senate, but there's no way the next vacancy gets filled by someone as liberal as Garland. If there was a Dem senate, both Ginsburg and Breyer would have to retire in the summer of 2017 to ensure a long run left wing SCOTUS majority and the backlash would likely turn the VA senate special into a repeat of the MA 2010 special.
It really comes down to whether at least 2 of Ginsburg, Kennedy and Breyer are still on the Court in 2021. If they are, then Dems are no worse off than with a narrow Clinton win, and if they are still on the Court in 2023, then they are likely better off, even if Trump/Pence is still president.