My reasoning is mostly what Beebo said. More for her own sake than anything else. She should spare herself, but it really is HER choice to make.
The choices everyone else makes will matter just as much. Given a supporting Congress, even an orange baboon can be effective.
The arguments against her running do not include this -
She should have won the race against the baboon with a street length in her favor, but she didn't.
No real reason to believe she would make it in 2020.
There are plenty of reasons to believe she could make it. Florida has enough disenfranchised voters suddenly returned voting rights to offset the margin she lost here. Pennsylvania elections are showing shifting winds still. Michigan and Wisconsin were also way too close to throw away as lost states. N. Carolina, Georgia, and even Texas are still turning more liberal, with getting out the vote having potential to do real damage.
Laugh at including Texas here, but the idea that Beto would come within 2% had people laughing too.
Nixon went from political laughing stock in the eyes of the public after historic losses to win the White House targeting the Electoral College.
History says it absolutely can be done.
She is more than capable for the Oval Office, but she has proven not to appeal enough to the Democratic half of the USA.
This is the most untrue statement of all.
Nobody can question that she had a healthy majority of the Democratic half of the USA with a straight face.
Having said all that, I still would rather not go through a repeat.
Whoever does run will still have to deal with people throwing the political powerhouses on the left under the bridge almost solely because it's the popular thing to do. The lack of a spine nowadays is more a problem of the electorate, not the ones running for office.