The town of Greenwich is considerably smaller than Connecticut’s biggest cities, but it ranks number-one in terms of registered Republicans – it’s the heart of the state’s GOP base.

It shares a border — and a similar profile — with Westchester County, N.Y., where in last week’s New York primary Donald Trump underperformed his statewide vote share, and John Kasich overperformed.


For those reasons, Greenwich is one of the key places to watch Tuesday, when five Northeastern states go to the polls in what’s been called the Acela Corridor primary. The landscape seems to favor the two national front-runners: Hillary Clinton and Donald Trump.

Both appear poised to add to their delegate leads, with polls suggesting each could pull off a five-state sweep. Clinton is well-positioned in the two biggest states voting Tuesday — Pennsylvania and Maryland — while Bernie Sanders' best hope of pulling out a win is either Connecticut or Rhode Island.

On the Republican side, where Trump has comfortable leads in every state, Ted Cruz and John Kasich are simply hoping to peel off a handful of congressional districts to make it harder for Trump to cobble together enough delegates to win the GOP nomination.

Here are 10 key places to watch as the results flow in Tuesday night:

Connecticut

Greenwich: If Kasich or Cruz can steal one of the state’s five congressional districts, it will likely be the affluent 4th District — where the Republican vote is anchored by wealthy and educated residents of Greenwich, Stamford and Bridgeport. In 2012, Mitt Romney ran about 10 points better in the 4th District than he did statewide.

New Haven: More votes came from New Haven than any other town in the 2008 Democratic primary, and it’s critical to Clinton’s effort to hold off Sanders — despite the fact she lost it badly four years ago.

In 2008, Barack Obama defeated Clinton by a more than two-to-one margin in New Haven, 66 percent to 32 percent — far greater than Obama’s 4-point margin of victory statewide.

New Haven is both a college town — it's home to prestigious Yale University — and easily the state’s most-diverse city. Sanders, who has won more than 70 percent of the under-30 vote thus far, will likely clean up with college students. He attracted an estimated crowd of 10,000 to a Sunday night rally there.

But if Clinton can turn out minority voters — fewer than one-in-three New Haven residents was non-Hispanic white, according to the 2010 Census — she can build a coalition of older whites and minority voters to put her over the top.

Delaware

New Castle County: By far the largest of Delaware’s three counties, New Castle accounted for 64 percent of the vote in the 2008 Democratic primary, and 47 percent in the 2012 Republican primary.

But New Castle is also split between overwhelmingly Democratic Wilmington, the state’s largest city, and the rest of the county. How Democratic is Wilmington? The city was 13 percent of the overall statewide electorate in the 2008 Democratic primary, but only 2 percent of the 2012 Republican primary.

Wilmington is majority-black: Obama beat Clinton there in 2008, 75 percent to 22 percent. But the race was much closer in the rest of New Castle County, with Obama only ahead by 8 points, 52 percent to 44 percent.

The state is winner-take-all on the Republican side — and while nearly half the vote will come from New Castle County, it functions differently from the rest of the state.

Mitt Romney won Delaware with 56 percent of the vote in 2012 — capturing 60 percent of the New Castle vote, but only 50 percent in Kent County and 55 percent in Sussex County.

Maryland

Baltimore city: Majority-black Baltimore city should be a boon for Clinton. Obama beat Clinton by a three-to-one margin in Baltimore City in 2008, but Clinton’s advantage among African-Americans against Sanders project well for her here.

Clinton could also benefit from a competitive mayoral primary also on the ballot on Tuesday, which could goose turnout in Baltimore city compared to some more suburban precincts.

Baltimore County: In the Republican primary — where delegates are allocated winner-take-all to the victor in each congressional district — Maryland’s tortuous congressional map makes it difficult to isolate specific regions. The district lines, which were drawn by Democrats to ensure a 7-to-1 party advantage in the congressional delegation, snake through communities in an effort to separate Republicans and keep them from having too much influence in a number of districts.

But Baltimore County is crucial for the GOP candidates. It touches two of the three districts anti-Trump forces think are the best chances to defeat the real-estate tycoon: the 3rd and 7th districts.

The majority-black 7th District is overwhelmingly Democratic and will be a key district for Clinton in her primary. But a small number of Republicans will also vote there, and both Cruz and Kasich are hopeful they can sneak ahead of Trump there.

The 3rd District snakes from the Baltimore Inner Harbor all the way down to Annapolis, but also includes a good chunk of Baltimore County. Anti-Trump groups are seeking to boost the more moderate Kasich there.

Montgomery County: The populous, liberal suburbs north and west of D.C. represent Sanders’ best chance to cut into Clinton’s big lead in the state. Obama carried Montgomery in 2008 by 12 points, a much smaller margin than his 25-point statewide edge.

Like in Baltimore with the mayoral race, a number of local contests could also boost turnout, including an expensive, closely fought primary for Congress in the 8th District, which includes most of Montgomery County’s immediate D.C. suburbs.

Pennsylvania

Allegheny County: Allegheny County, which includes Pittsburgh and the immediate suburbs, holds more GOP voters than any other county in the state.

Pennsylvania’s “loophole primary” makes the focus on specific districts for Republicans trickier, but Allegheny is still a key battleground. Kasich was born and raised in the county, in McKees Rocks. Trump visited Pittsburgh earlier this month.

The county includes all or part of three different congressional districts: the 12th, 14th and 18th.

On the Democratic side, Allegheny is battleground territory: Clinton won it by almost nine points in 2008. A similar performance there on Tuesday could close the door on Sanders’ underdog bid at a statewide victory.

Lackawanna County: This is Clinton territory: She won Lackawanna by a yawning margin in 2008, 74 percent to 26 percent.

Clinton claims Scranton roots that served her well eight years ago. And it’s no surprise one of her closing events in the state was in Dunmore, just outside Scranton, last Friday. (Her husband held an event earlier this month at Scranton High School.)

These are mostly white voters who stuck with Clinton eight years ago. The question is whether they will still serve as a firewall for her on Tuesday, or jump to Sanders, as a number of white Democrats have in other states.

Philadelphia: Clinton managed to win statewide eight years ago despite losing Philadelphia by nearly a two-to-one margin, 65 percent to 35 percent.

This time around, the African-American base in Philadelphia should be strong for Clinton. But the city is also a big college town, and enhanced youth turnout could help Sanders.

Clinton has the backing of former Mayor Michael Nutter — who backed her over Obama in 2008 — and also from longtime supporter Ed Rendell, another former Philadelphia mayor and former two-term governor, who will be under pressure to reinstate his turnout machine to help the former secretary of state.

Rhode Island

Warwick: Providence, the state capital, should function much like Philadelphia but scaled down. Obama narrowly won in Providence in 2008; Sanders will need to turn out enough young voters — including students at Brown University and Providence College — to overcome Clinton’s advantages with non-white voters.

But Warwick, the state’s second-largest city, also looms large. Clinton won comfortably here eight years ago, beating Obama, 61 percent to 38 percent.

The city is mostly white, but the population leans older, which could benefit Clinton.