By A.T. Janos (staff@latinospost.com) | First Posted: Sep 12, 2013 03:49 PM EDT

Democratic party leaders began rallying behind mayoral frontrunner Bill de Blasio on Thursday, urging second-place primary finisher Bill Thompson to step out of the race in the name of party unity.

Under New York City election rules, an automatic runoff between the top two candidates in a primary occurs when no one candidate gets above 40 percent of the total vote. With 99 percent of votes counted, de Blasio currently has 40.3 percent of the vote; however, with absentee ballots still arriving, the possibility remains that the public advocate may fall just short of the benchmark.

Still, several signs indicate that Thompson faces an uphill fight that would, ultimately, prove fruitless. De Blasio put together a broad coalition of voters, including a plurality of black voters that Thompson had counted on to be his base of support.

On the Republican side, former Metropolitan Transit Authority commissioner Joe Lhota defeated billionaire businessman John Catsimatidis, creating all the more pressure for Democrats to rally around their strongest candidate. Registered Democrats outnumber Republicans 6-to-1 in New York City, but the city has not had a Democratic mayor since 1999.

The New York Times reports several large unions that had backed other opponents rallying around de Blasio in an attempt to pressure Thompson and avoid a protracted run-off race. On Wednesday night, endorsements rolled in from Local 32 BJ (i.e. doormen) from the Service Employees International Union, and the Retail, Wholesale and Department Store Union. Both unions previously backed third place finisher Christine Quinn.

Were a run-off to take place, it would be slated for October 1st, several weeks away. The general election, held November 5th, is a quick pivot thereafter.

A runoff is estimated to cost the city $20 million in expenses. Currently, the only confirmed runoff is for Public Advocate, between City Council member Letitia James and state Senator Daniel Squadron.

The total operating cost of that office is $2.3 million dollars, or just over 11 percent of the cost of the election to determine it.

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