Tuesday was not a good day for Hillary Clinton's campaign.
Worse yet, Quinnipiac University released a series of polls from three key swing states with bad news for Clinton. The poll results showed Donald Trump with a 4-point lead over Clinton in Ohio and in a statistical tie with her in Pennsylvania and Florida.
Most political analysts and pundits, myself included, have predicted that Trump is highly likely to lose the general election. The Quinnipiac poll results and West Virginia election outcome won't change that consensus.
But Tuesday is a reminder that Clinton is far from a strong candidate in her own right.
How flawed is Clinton?
The significance of Tuesday's election returns and poll results should not be overstated. Clinton emerged from the West Virginia primary with enough delegates to come within striking distance of the 2,383 she needs to formally secure the Democratic nomination.
And the Quinnipiac surveys relied on questionable assumptions about the 2016 electorate. In particular, the Quinnipiac polls projected that minorities would constitute a smaller share of the electorate in 2016 than in 2012. That is a highly debatable proposition when the GOP nominee is the most divisive and polarizing presidential candidate in modern history.
In 2012, polls that underestimated minority turnout correspondingly overestimated Mitt Romney's appeal. For example, four years ago, the Quinnipiac poll showed Romney leading Barack Obama in Florida, but high minority turnout enabled Obama to win the state in November.
It's also worth noting that this week's Quinnipiac polls are not reflective of other polling data. If one looks at the overall average of all recent polls, Clinton leads Trump by 4 in Florida, by 7 in Pennsylvania and by 3 in Ohio.
Nevertheless, it is undeniable that Clinton remains a flawed candidate. Here are four of her biggest vulnerabilities:
1. A poor public image
One of the ironies of Hillary Clinton's career is that she first got into public life as a House Judiciary Committee attorney assigned to the Watergate investigation. But in her own political career, she has been plagued by one scandal after another: Whitewater, Travelgate, the Clinton Foundation and now the uproar over her State Department emails.
The scandals aren't her only image problem. In an age when presidents are expected to be funny and informal, Clinton has never developed a relaxed and straightforward public demeanor, particularly on television. Her image problems have taken a severe toll on her approval ratings as over 50 percent of Americans now view her unfavorably. Only Trump is viewed more negatively by voters.
Even fellow Democrats worry that she comes across as inauthentic. Former Obama adviser David Axelrod warned last year that Clinton "needs to untether herself from the teleprompters and talking points and genuinely interact in real terms with people."
That's far easier said than done. One doesn't just flip a switch and become "natural" overnight. And Trump has made clear that personal attacks on Clinton will be a central and unrelenting theme of his campaign.
2. Liberals still feeling the Bern
As Trump unleashes his character attacks, Clinton will need Democrats to rally to her side.
But to unify the party, the Clinton campaign must reach out to white liberals more effectively than it has thus far. Although Clinton has won overwhelming and critical support from minority voters, she still has a long way to go to win over the white liberals who form the core of Bernie Sanders' base.
To be sure, fear of a Trump presidency will undoubtedly motivate most Sanders Democrats to vote for Clinton in the fall. Moreover, she recently came out with proposals for subsidized child-care programs and a plan to allow middle-aged Americans to purchase Medicare coverage that will appeal to Sanders voters.
But with Trump taking volatile, unpredictable and incoherent stands on everything from the minimum wage to the national debt, the normal ideological lines will be heavily blurred in the 2016 campaign.
Until Clinton articulates a clear policy vision that unites all wings of the Democratic Party, her left flank will remain a potential vulnerability.
3. Working-class whites
Clinton has no chance of winning a majority of working-class white voters. They have voted heavily Republican for years, especially working-class men. In the 2014 midterm elections, for example, working-class whites voted for Republicans by a 30-point margin.
But Clinton needs to win some of them. In 2012, Barack Obama won the support of about 35 percent of working-class whites, which was enough to help him win re-election.
One of the more surprising aspects of Clinton's primary campaign has been her failure to focus on working-class women. Trump's 70 percent unfavorable rating with women, combined with Clinton's newfound populism on economic issues, gives her a real chance to make inroads with at least some working-class voters.
But if she lets Trump position himself as the tribune of the working class, she'll only dig a deeper hole for herself with blue-collar voters.
4. American prejudice
Donald Trump is running a campaign that is dividing Americans along racial, religious and gender lines.
The tactics of divide-and-conquer have certainly worked in the past. For example, the GOP's Southern strategy, which stoked the fears and resentments of white voters, contributed to Republican victories in five of the six presidential elections between 1968 and 1988.
As the 2012 election results demonstrated, changing demographics have made the Southern strategy far less effective than it once was. When Ronald Reagan won in 1980, 80 percent of Americans were white. Today only 62 percent of Americans are white.
But Clinton cannot take a backlash against Trump for granted on the assumption that it will simply happen automatically.
To win a national majority, the Clinton campaign will need to build a biracial coalition of voters along the lines of the Obama campaigns in 2008 and 2012. Those campaigns worked because Obama was one of the most effective campaigners in modern American political history.
Thus far, however, Clinton has not been a particularly effective or inspired communicator on the campaign trail. She has had solid debate performances but has not offered a single memorable speech during the 2016 campaign. In an election that will likely strain American unity like no other in recent years, Clinton's coalition-building skills will be put to the test.
Campaign quality matters
But Sanders' victory in West Virginia underscores the extent of Clinton's own vulnerabilities as a candidate. The 2016 election is extremely winnable for Clinton, but the White House won't be handed to her.