While Hillary Clinton is likely to grab the Democratic nomination, she still faces a tough challenge from Senator Bernie Sanders, calling into question how she will fare in the US presidential race.

Clinton lost to Sanders in Tuesday's Democratic primary in the state of West Virginia, a mostly white working class state.

So far the former secretary of state has had a tough time with Sanders, who has beaten her in several states.

Indeed, the last several months have seen Sanders draw large and enthusiastic crowds to his rallies.

The senator from Vermont has particularly strong support among millennials, who continue to feel the sting of the 2008 economic crash, and who are fed up with Washington elites who they believe have not helped them.

"Clinton is having a difficult time with Sanders. (Sanders) continues to run well among white men and young people," Brookings Institution's senior fellow Darrell West told Xinhua.

Critics say that recent losses to Sanders underscore what they call Clinton's weakness as a candidate, and wonder what her troubles with Sanders say about her ability to beat the presumptive Republican candidate Donald Trump in the general election.

"It does point to a challenge her candidacy will face," Julian Zelizer, professor of history and public affairs at Princeton University, told Xinhua, speaking about the general election.

There is concern within the Clinton camp about how strong her support will be with white male middle-class voters in states like Pennsylvania, West Virginia and Michigan, Zelizer said.

"The Trump camp certainly sees an opportunity to do well in swing states," Zelizer said, referring to the coming Trump vs Clinton race to the White House.

Zelizer said whether white working-class Democrats will defect to the Trump camp remains unclear.

"That is not clear. (Trump) certainly has shown some appeal, though the battle lines have not yet been drawn and the Democrats have not yet gone after (Trump's) economic record or that of the Republican Party," he said.

Many, probably most, Sanders supporters "are in a very different ideological place than Republicans," he noted.

West said white men and young people are two groups where Clinton needs to run better in order to win the general election.

"Trump is making a big pitch for white men, whose wages have stagnated over the last 30 years. She (Clinton) needs to explain to those voters how her policies will help them," West said.

"Right now, they seem skeptical of what she will do and that creates an opportunity for Trump," West said.

Trump wants to peel off disaffected Democrats and Independents, and put the big industrial states such as Ohio, Michigan and Pennsylvania into serious contention for Republicans, he said.

Which candidate unions will support is another question. While most will likely stay true to their record of backing Democrats, Trump may have an edge with construction unions.

Trump has good relations with construction unions and he is talking a lot about the need to revive US manufacturing, so he has an opportunity with manufacturing unions to win their support, West said.

"They will want to hear in greater detail how he plans to save manufacturing jobs and make the US more competitive globally," West said.

Zelizer believed the unions will support the Democratic candidate.

"The Democrats have been much more sympathetic to their issues and there is a minimal chance that Trump can really make a dent into this advantage," he said.

The author is a writer with the Xinhua News Agency. The article first appeared on Xinhua. opinion@globaltimes.com.cn