Who will win in 5 states?

Republican presidential candidate Donald Trump signs an autograph for a supporter at a campaign rally at West Chester University, Pennsylvania. Photo / AP

Five states in the Northeastern US will go to the polls tomorrow as Donald Trump and Hillary Clinton look to cement themselves as their parties' presumptive nominees.

Polls show Trump and Clinton leading in all five of the contests, but the stakes remain high as Trump walks a tightrope in search of the 1237 delegates needed to win the nomination outright, and Clinton looks to - at last - see off the challenge from Bernie Sanders.

The Republican front-runner is expected to sweep tomorrow's slate, but the margins of victory will be key as the delegates are portioned out between Trump, Ted Cruz and John Kasich.

The Sanders campaign, meanwhile, has said the results will determine whether they are full steam ahead moving towards the convention in July, or begin the process of uniting the Democratic Party.

Here's the state by state breakdown:

1 Pennsylvania

The biggest prize on offer, Pennsylvania will award 17 delegates to whichever Republican wins the state - that will almost certainly be Trump. A bizarre arrangement means that the remaining 54 delegates will be unbound at the convention in July, but the better a candidate does in the primary election the most hand-picked delegates he can send to the convention. For the Democrats, Pennsylvania is worth a whopping 189 delegates to be awarded proportionately. Clinton is expected to take the lion's share.

2 Maryland

The statewide winner on the Republican side will win 14 delegates, with the remaining 24 being allocated to the winners in each of the state's Congressional districts. Trump could win anywhere from 26 to all 38 delegates. The Democrats will award 118 delegates in Maryland with Clinton, again, expected to take most.

3 Connecticut

Like in neighbouring New York and Massachusetts, Trump is expected to dominate in Connecticut. The big question is whether he can hit the 50 per cent threshold and thereby take all or nearly all of the state's 28 delegates. If not, they will be allocated proportionately and Trump will miss a chance to narrow the gap to 1237. Polls show Sanders within striking distance of Clinton in the Nutmeg State. A win here would help him make the case that the race is still on.

4 Delaware

Though a small state, Delaware awards its delegates in a winner-take-all format. Trump is all but guaranteed to take all 16. Another state where Clinton is expected to win, but Sanders is close enough to hold out hope for an upset.

5 Rhode Island

The outcome is proportional, with Trump is expected to take just over half of the 19 delegates on offer. This is perhaps Sanders's best chance to pull out a win, with the most recent poll showing him in the lead. If he doesn't fare well elsewhere it may be too little too late.