In the related question What do Democrats have to gain, politically, by preventing Brett Kavanaugh's appointment to the Supreme Court? various aspects of how the Democrats benefit from delaying the nomination are discussed. But why can't the Republican party simply go ahead and force a vote on the nomination, just like they did during the hearings for Neil Gorsuch?
This would strip the Democrats of any advantage they might currently have and ensure the Supreme Court is stacked with Conservative nominees regardless of how the election turns out in November.