From Gwen Graham - THIS is the way to do it!

[mythology]

32. You should direct the snark to the people above

They are making the claim, one that looks rather laughable if you consider a higher proportion of Sanders 2016 primary supporters voted for Clinton in the 2016 general election than Clinton 2008 primary supporters voted for Obama in the 2008 general election. In fact Sanders supporters were in line with historical averages of about 10%. If they want to assert that Clinton lost because Sanders didn't concede as quickly as they like, they need to support the assertion rather than just stating it as a fact.

https://www.npr.org/2017/08/24/545812242/1-in-10-sanders-primary-voters-ended-up-supporting-trump-survey-finds

A more important caveat, perhaps, is that other statistics suggest that this level of "defection" isn't all that out of the ordinary. Believing that all those Sanders voters somehow should have been expected to not vote for Trump may be to misunderstand how primary voters behave.
FACT CHECK: 10 Statements From Trump's Phoenix Speech
Politics
FACT CHECK: 10 Statements From Trump's Phoenix Speech

For example, Schaffner tells NPR that around 12 percent of Republican primary voters (including 34 percent of Ohio Gov. John Kasich voters and 11 percent of Florida Sen. Marco Rubio voters) ended up voting for Clinton. And according to one 2008 study, around 25 percent of Clinton primary voters in that election ended up voting for Sen. John McCain, R-Ariz., in the general. (In addition, the data showed 13 percent of McCain primary voters ended up voting for Obama, and 9 percent of Obama voters ended up voting for McCain — perhaps signaling something that swayed voters between primaries and the general election, or some amount of error in the data, or both.)

Some studies show a negative impact of a contentious primary - although it specifically looked at southern states with runoff voting, not necessarily representative of the U.S. as a whole. Others like 538, don't see a strong relationship.

https://www.vox.com/2016/5/5/11593668/close-primaries-general-election

https://fivethirtyeight.com/features/sanders-shouldnt-drop-out-for-clintons-sake/