Bernie Sanders' solid primary victory in West Virginia didn't appreciably cut into Hillary Clinton's comfortable delegate lead in their fight for the Democratic presidential nomination. But it did further fuel lingering doubts about the scope and intensity of her support within her own party heading toward the general election against Donald Trump.
With the likelihood that Senator Sanders will keep racking up primary victories into June, Ms. Clinton faces continuing questions among hard-core liberal Democrats about whether the lack of fervor for her could be her undoing in November.
There can be little doubt of the loyalty of the huge army of Democratic women that has mobilized behind her candidacy ever since her run against Barack Obama in 2008. But her competition with Mr. Sanders this year has drawn a sharp contrast between his call for a political revolution and her more tempered gradualist call for social change and progress.
While many analysts have credited Mr. Sanders with pulling Hillary Clinton to the left, in reality on some major issues she has clung to the Obama social agenda. As Mr. Sanders calls for replacing the president's health care reform that now popularly bears his name, Ms. Clinton warns that starting over would not survive stiff opposition in Congress, already weary of arguing over Obamacare.
In the competition to lead the Democratic charge to rescue the middle class from its declining fortunes, Mr. Sanders calls flatly for raising the federal minimum wage from $7.25 an hour to $15. Ms. Clinton essentially says she also favors it, but believes it should be boosted gradually, based on local circumstances.
She cites the party's proposal in her adopted state of New York to raise the rate from $9 to $12 and then eventually to $15. But it has been a weak argument in debates with Mr. Sanders and may well be one position on which she may have to yield to reassure Mr. Sanders' supporters in the fall campaign, assuming she will be facing Mr. Trump then.
Mr. Sanders' ability to score repeated primary victories over Ms. Clinton, especially in states that permit independents to vote in their Democratic contests, underscores her need to focus on the broader general-election field and the Obama constituency she hopes will stick with her.
Right now, her strongest appeal to that field may simply be that she is not Donald Trump, given the tempest he has stirred up all this year with his intemperate campaign eruptions against women, Muslims, Mexicans and other foreigners, as well as his hostile views on American foreign policy assistance. As Ms. Clinton pointedly pivots her campaign to focus on Mr. Trump despite the fact that Mr. Sanders is still contending for the nomination, she risks an air of presumption that could alienate Sanders supporters she will need in general election. Mr. Trump in turn seems more than willing to take her on right now, as well as her surrogate husband over his presidential indiscretions and her own role, as Mr. Trump puts it, as his prime "enabler."
All this can cast a shadow of doubt over what most public-opinion polls have been interpreted as indicating a sure-fire Clinton defeat of Mr. Trump in November — in a year in which polls have taken a general beating in credibility, resulting from wild errors in various state primaries.
So the stubborn revolution of Bernie Sanders, in which he refuses to say he is beaten and insists he still has a path to victory, though admittedly a narrow one, presses on. The manner in which he continues against all odds to demonstrate uncommon support among young and older voters through huge rally turnouts remains a burr in Ms. Clinton's side.
All the usual yardsticks of victory are there for her, including a sharp split among Republicans over their controversy-stirring presumptive nominee. But as Hillary Clinton approaches her own nomination in July, the Sanders phenomenon remains a nagging question about her own electability in the fall.
Perhaps her anticipated nomination in Philadelphia will clear the air by achieving a convincing accommodation with the "revolutionary wing" of her party, thus joining the fervor to rid the country of Donald Trump along with the desire to elect its first woman president.
Jules Witcover is a syndicated columnist and former long-time writer for The Baltimore Sun. His latest book is "The American Vice Presidency: From Irrelevance to Power" (Smithsonian Books). His email is firstname.lastname@example.org.