West Virginia's primary was a good victory for Bernie Sanders. Good, but not nearly good enough.

The 74-year-old Vermont senator will nevertheless soldier on in what looks to be an increasingly unattainable goal to clinch his party's presidential nomination. But the longer this fight drags on, Democratic strategists warn, the more it could end up hurting Hillary Clinton and the party's chances of keeping one of its own in the White House.

Even before Tuesday night's outcome, Clinton's delegate dominance put her far enough ahead that she could afford to lose every remaining primary and still win the Democratic nomination in July. The former secretary of state had a popular-vote advantage of three million votes over Sanders, and was ahead by 300 pledged delegates.

Sanders has remained defiant despite his slimming odds.

"Don't let anybody tell you this campaign is over," he boomed earlier this week, vowing to take the battle through to the Democratic National Convention in July and to "fight for the last vote we can find." At another campaign event, he repeated familiar criticisms of Clinton's lucrative speeches to Wall Street and her support for the 2003 invasion of Iraq.

U.S. Democratic presidential candidates Hillary Clinton and Bernie Sanders are still engaged in a heated battle despite the fact Sanders has little chance of securing the party's nomination. (Jonathan Ernst/Reuters)

But as Clinton shifts her game plan to the general election, Sanders may need to check the power of his own rhetoric, says Washington-based Democratic campaign strategist David Wade.

"I cannot believe he wants to be remembered as someone who wrote scorching attack lines that are going to be recycled by Donald Trump," Wade said.

Those aren't just the musings of a pundit.

Trump has already seized on Sanders's remarks questioning Clinton's judgment for her Iraq war vote.

"When he said, 'Bad judgment,'" Trump told MSNBC's Morning Joe, "I said, 'Sound bite!'"

Trump boasted that he would be "taking a lot of the things Bernie said, and using them" against Clinton.

"I can reread some of his speeches and get some very good material," the billionaire real estate tycoon told the MSNBC hosts.

'Throwing grenades' inside the tent

Wade believes that's the kind of political opportunism the Democratic Party needs to block if it's to present a strong, unassailable candidate to take on Trump in November.

"If you're Hillary Clinton, you're going into a time when Donald Trump is going to be on the attack every day in unpredictable and maybe ugly ways," he said. "You're going to the point where it's not going to be helpful to the party to have someone throwing grenades from the sidelines and inside the tent."

Wade encountered similar frustrations in 2004 when he worked to secure the Democratic nomination for John Kerry, who lost in the general election to George W. Bush.

When he ran for president in 2004, John Kerry was under attack from Democratic candidates who had yet to give up their fight for the party's nomination as well as the Republican nominee, George W. Bush. (Brian Snyder/Reuters)

"It was clear he was going to be the nominee," Wade said, recalling that the Bush campaign had started attacking Kerry while some of Kerry's Democratic opponents were still doing the same.

"You had a little bit of this feeling, like you're drinking out of the fire hose trying to build a general election [strategy], and that's harder to do when you still have primary opponents with the riot hoses spraying at you full blast."

Time for party unity

Competitive nomination campaigns are generally viewed as beneficial for a candidate, offering a chance for some spring training and debate preparation, says political operative Mike Cuzzi.

But Cuzzi, who worked for Barack Obama's campaign for the 2008 Democratic nomination, says when a candidate's chances of winning are no longer mathematically realistic, it's time to pivot towards party unity.

"That doesn't mean the candidate who's trailing should get out of the race," Cuzzi said. "It's perfectly appropriate for them to stay in the race, raise their issues and use the bully pulpit that the campaign affords them to influence the dialogue."

Sanders has, at various points, hinted at a willingness to do just that, reminding voters that his campaign is about more than just winning, it's about moving the country in a new political direction.

He may have succeeded in that regard by energizing a more liberal base and nudging Clinton to the left, says Robert Watson, an American studies professor at Florida's Lynn University.

Robert Watson, an American studies professor at Florida’s Lynn University, says Hillary Clinton could probably use some time to rest before the general election campaign heats up. (Don Emmert/AFP/Getty Images) "Hillary was initially avoiding issues like Wall Street, the minimum wage, even guns," said Watson, who studies the American presidency. "With Bernie, she had to really adequately address her Wall Street speeches because Bernie keeps bringing it up. She's had to go to the left on supporting regulation on Wall Street, reiterating her support for the stimulus. And she saw an opening to outflank Bernie on gun control on the left."

Sanders has arguably strengthened Clinton's candidacy, Watson says. But so long as he continues to attack her for big-money donations and bad judgment, he risks souring her potential voters in the lead-up to November.

Meanwhile, campaign funds are being depleted. The Sanders team laid off more than 200 workers late last month, in perhaps the biggest sign yet that the campaign is winding down.

And then there's the physical toll to consider.

Presuming she becomes the nominee, a primary-season slog could deny Clinton some rest time before the general election.

"You hear it in her voice. It's become hoarse," Watson said. "I don't think she's recovered it … and you can imagine she'd like to by now put this thing to bed and give a few thank-yous, but she's still out there on the campaign stump fundraising."

Clinton, who herself battled Obama to the bitter end during the 2008 primary contest, is in no position to complain about Sanders refusing to quit.

"I respect Senator Sanders and whatever choices he's making. And I have a lot of empathy about this," she told CNN.

Things may be a little more fraught behind the scenes.

An eyebrow-raising message landed in the inboxes of Sanders email subscribers on April 20, the day after Clinton trounced him in the New York primary.

Sen. Bernie Sanders continues to rally supporters around a vision for America that differs from that of Secretary Clinton's campaign. (Win McNamee/Getty Images) "F—k him," read the subject line. The two-word quote was attributed simply to a "Clinton aide."

The Sanders campaign, which sent out the email signed by campaign manager Jeff Weaver, apologized for the "salty language."

But it wanted to make Sanders supporters aware of an "outrageous" report from Politico. An unnamed Clinton staffer, the report said, expressed growing frustration with Sanders's refusal to soften his attacks against Clinton and "tone it down," given that she now appeared to be the presumptive nominee.

The Sanders organization then doubled down.

"We're not going to stop talking about our corrupt campaign finance system, the danger facing our climate and our planet, and the influence of Wall Street," Weaver's email said. "Bernie is not going to stop talking about how his vision for America differs quite significantly from that of Secretary Clinton."