MILWAUKEE — Weeks of Democratic pressure on President Joe Biden to drop out of the presidential race had already turned the 2024 campaign on its head right as Republicans were readying to gather this week and crown former President Donald Trump as their nominee.

Then a would-be assassin grazed Trump’s ear with a bullet at a Pennsylvania rally.

Both developments have shaken up a race that had remained stagnant — but close — for months, and they will be top of mind for attendees going…