According to a recent survey, voters prefer to pick their party's presidential candidate directly.
The Republican presidential hopeful has been severely criticised for his views on sensitive topics.
Despite losing Rhode Island Clinton added at least 178 delegates before full results were reported.
Sanders took home a surprising victory in Rhode Island, robbing Clinton of a five-state sweep.
There are 36 Republican delegates and 213 Democratic delegates up for grabs in the two states.
There are 82 Republican delegates and 171 Democratic delegates up for grabs in the two states.
Sanders made the comments during a campaign stop in Baltimore, Maryland ahead of the 26 April primary.
The building later turned blue to announce Hillary Clinton's Democratic primary win.
Wins give campaign boost ahead of the 26 April primaries in 5 states.
The Empire state has a large cache of delegates with 95 for the GOP and 247 for Democrats.
There are 95 delegates available to Republicans and 247 delegates available to Democrats.
Sanders called the pontiff one of the extraordinary figures in the world.
Most raucous debate yet spurred on by wild cheers and hisses from the New York crowd.
Democratic frontrunner is accused of campaigning in a train carriage.
Sanders and Clinton will vie for 14 Wyoming delegates ahead of the all-important New York primary.
Both candidates believe they can surpass the party frontrunners to nab the nominations in July.
42 Republican delegates and 86 Democratic delegates were up for grabs in Wisconsin.
There are 86 delegates available to Democrats and 42 delegates for Republicans in the next primary.
Sanders' message is that real change is possible, but Clinton basically says that this is as good as it gets.
Vermont senator headed for victory margins of over 50 percentage points in both states.
Speech by Vermont senator disrupted by bird swooping onto podium in Portland, Oregon.
There are 142 delegates at stake for the remaining two Democratic presidential candidates.