How to Make It
Combine sugar and 1 cup water in a small saucepan. Bring to a boil, stirring, until sugar dissolves, about 4 minutes. Remove from heat. Add grapefruit juice, Campari, gin, and sweet vermouth and stir to combine.
Place 2 half-slices of grapefruit in each of 10 3-ounce ice pop molds and top with grapefruit juice mixture.
Insert sticks and freeze until firm, at least 4 hours and up to 1 week. To unmold, dip molds in cold water to soften very slightly and remove pops. Transfer to a parchment-lined baking sheet and keep in the freezer until just before serving.