After months of speculation, State Sen. Phil Boyle, the designated Republican candidate for Suffolk County sheriff, has closed the door on a possible Democratic cross-endorsement.

Boyle acknowledged that he signed an affidavit at the party’s convention Monday night pledging not to take the Democratic line. On the night of the GOP convention, he said he was unaware of any pledge document. However, he took a photo of the papers and realized he signed the pledge.

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“As a lifetime Republican, I do not intend to run on the Democratic line,” Boyle said.

The GOP used the pledge affidavits for the first time after the party two years ago changed bylaws to bar Republicans from taking another major party line in nonjudicial races. John Jay LaValle, Suffolk GOP chairman, told those at the convention he would tear up the nomination acceptance of any candidate who did not take the pledge.

Speculation about a cross-endorsement arose because Suffolk Democratic chairman Richard Schaffer said he was “open” to backing Boyle, although the party named retired New York City police officer Dan Caroleo as its candidate.

Rick Brand