Hillary Clinton is on track for another big night

Hillary Clinton appeared on her way to a strong night in five states' primary contests Tuesday.

Shortly after the polls closed on Tuesday, several major news outlets called Maryland for Clinton.

And polls conducted before Tuesday's primary contests showed the former secretary of state leading rival Sen. Bernie Sanders.

Tuesday's wins could put Clinton even closer to securing the Democratic nomination. FiveThirtyEight's Nate Silver reported that going into Tuesday's races, Sanders already needed to capture 58% of the remaining pledged delegates to secure a pre-convention majority.

As Clinton has maintained her large delegate lead, the former secretary of state's campaign has increasingly questioned Sanders' path to the nomination.

Speaking to reporters after Clinton's primary victory in New York last week, communications director Jennifer Palmieri said Sanders needed to prove how he could win the nomination going forward.

"We do think that it is certainly within his right to go all the way," Palmieri said, referencing Sanders' pledge to continue campaigning until the Democratic convention. "But we hope that at the end of the contests, she will lead the popular vote, she will lead in pledged delegates. At that point, they will have to prove to you how they will win the nomination."

Sanders' campaign staff already appears to be shifting its message.

Senior adviser Tad Devine told The New York Times that Sanders may stay in the race through the remaining Democratic primaries - but added that he is likely to "reassess" his campaign strategy going forward.