While Mitt Romney has been deemed the Republican frontrunner in the wake of Rick Santorum's decision to drop out of the GOP race for the White House, Tuesday is the first chance for Romney to prove that in five different primaries.

In other words, if Romney sweeps Pennsylvania, New York, Delaware, Connecticut and Rhode Island - along with most of the delegates - that's what he is supposed to do.

But, if Romney stumbles, with Ron Paul and/or Newt Gingrich holding his vote totals and delegate numbers down, then there will be Rumblings of Trouble on the GOP side.

Paul has been holding a string of events in recent days that hold a very familiar story line, as thousands turn out for him in good and bad weather.

But we have seen this before, when it doesn't translate into big results at the ballot box.  Maybe it will be different this time.

Paul's forces have done very well in some of the recent caucus rounds, winning a big chunk of delegates in Minnesota, Colorado and a few other states.

As for Newt Gingrich, he keeps campaigning and piling up the campaign debt, which stood at over $4.5 million at the end of March.

Gingrich has focused a great deal on Delaware, actually turning some Romney endorsements into Newt backers.

These five primaries come down to one thing - turnout. Can the Romney campaign motivate people to vote when they think Romney already has this in the bag?

We have certainly seen protest votes before. I always think of 1992, when Jerry Brown beat Bill Clinton in Connecticut after Paul Tsongas got out of the race.

But Brown's victory in the Nutmeg State was a short-lived boost for his campaign, as Clinton knocked him out soon after with a win in New York.

(My best memory of that 1992 primary in New York was Brown's people organized a bus to carry reporters to a series of stops in and around Manhattan. We boarded the vehicle and were ready to go when the driver suddenly stood up and announced that the Brown Campaign had not paid him, and so this bus wasn't going anywhere. And it didn't.)

As for tonight, here's a rundown of the delegate selection rules and the number of delegates at stake:

* Rhode Island - 16 delegates, proportional by the two congressional districts
* Connecticut - 25 delegates, 15 will be winner-take-all by congressional district (5 each); 10 statewide delegates are winner-take-all if you get over 50%, otherwise they are proportional with a 20% threshold
* Delaware - Pretty simple here, if you win statewide, you win 17 delegates. No requirement to get over half the vote, just the final winner.
* New York - 92 delegates at stake, with winner-take-all locally, as the 29 congressional districts award two delegates to the winner of each district. The 34 statewide delegates are winner-take-all if you get over 50%, otherwise it is a proportional result with a 20% threshold.
* Pennsylvania - 59 delegates are elected directly by the voters, as delegate slates are on the ballot along with the non-binding Presidential beauty contest vote. Five of Pennsylvania's 18 congressional districts have 4 delegates at stake, the rest have three.

There you have it - 209 delegates at stake to the Republican convention from five states.

Make sure to join me tonight on Twitter @jamiedupree for insights into the Republican primary numbers.