CAPITOL HILL—

Democratic lawmakers have told VOA they are now assuming a presidential contest pitting Hillary Clinton against Donald Trump, while some Republicans still cling to hopes their party will nominate someone other than the New York businessman.

The assessments came one day after Trump swept five primary contests and former secretary of state Clinton won four. Both front-runners dramatically expanded their respective delegate leads, although they did not clinch their party's presidential nomination.

"I think it's pretty clear that it's going to be Donald Trump against Hillary Clinton," said Democratic Senator Ed Markey.

"The results for Secretary Clinton were so strong that it is very plain she will be our nominee," said another Democrat, Tim Kaine.

"On the Republican side, the five-for-five [Trump victories] makes it more likely that Mr. Trump will be over the threshold when he goes to [the Republican National Convention in] Cleveland, or he will have such a lead that it would be very difficult for him to be thwarted," Kaine added.

Among Republican lawmakers, perspectives differ as more primary contests loom.

A supporter for Republican presidential candidate Donald Trump holds up a sign during a campaign stop, April 20, 2016, in Indianapolis, Indiana.

"If you want to stop Trump, we'd better win Indiana, and [challenger Ted] Cruz and [challenger John] Kasich better coordinate their strategy regarding California," said Republican Senator Lindsey Graham. "We have to be all hands on deck when it comes to the remaining primaries. If we can stop him [Trump] in Indiana, we've got a chance."

Republicans opposed to Trump are banking on a contested convention in which the businessman fails to win the nomination outright, and delegates coalesce around an alternative after a first round of balloting.

Graham says such an outcome is not without precedent.

"With [former president] Abraham Lincoln, we [Republicans] picked the guy that finished second, not the guy that finished first," Graham said. "So if it was good enough for Abe, then it would be good enough for [Ted] Cruz, or whoever we pick second."