Spotted on Hylan Boulevard: a large, mobile billboard with President Donald Trump and his choice for Congress, Dan Donovan, urging Republicans to vote on Tuesday. 

Over in Michael Grimm's office, volunteers work the phones. 

Both campaigns are shifting into high gear. 

"We are spending a lot of time across the entire district," said Jessica Proud with the Dan Donovan campaign. "Again, hitting 25,000 doors this weekend and leaving no stone unturned."

"We're going to have close to 10,000 IDs on election day for the primary, and we are going to pull them all out," said Joe Shikhman with the Michael Grimm campaign.

The intensifying activity reflects the high stakes in the district, which is seeing its first contested Republican primary in eight years, when barely 14,000 people cast votes.

There are nearly 118,000 registered Republicans in the district. Only a fraction are expected to vote. 

"So one would expect turnout to be in the 20 to 30 percent range," said Richard Flanagan of the College of Staten Island. "Maybe it will be higher because it is such a contested election."

With voter turnout low, we will be watching a couple of key areas in the district on Tuesday.

Grimm’s base is on the east shore of Staten Island, areas that were hit hard by Hurricane Sandy. He will likely do well there.

The south shore, which has a large concentration of Republicans, is expected to be a crucial battleground. Who does well there could be a good indication of who wins on Tuesday.

The Brooklyn side of the district is seen as a Donovan stronghold. If he doesn't do well there, he could be in trouble.

Observers say the lower the turnout, the better it will look for Michael Grimm, seen as the outsider here with an energized base. The higher the turnout, the better it will be for Dan Donovan, meaning his institutional support got out the vote.