Chris Cillizza

House Speaker Paul D. Ryan's refusal to endorse presumptive Republican presidential nominee Donald Trump sent the ongoing debate over whether the real estate billionaire can unite the party against Hillary Clinton in the fall election into overdrive.

If Hillary Clinton wins Florida and carries the 19 states (plus D.C.) that have voted for the Democratic nominee in each of the last six elections, she will be the 45th president. It's that simple.

Sarah Palin went to Wisconsin over the weekend to tout Donald Trump at a GOP fundraising dinner in advance of the Badger State's presidential primary today. Her speech was awkward and riveting at the same time.

The biggest day - and night - of the 2016 presidential primary season is in the books. Voters in 11 states, from Texas to Vermont, cast ballots with hundreds of delegates at stake on both sides.

The real fight emerged in the battle for second and third place among establishment Republicans desperate to grab a top-tier slot heading into the South Carolina primary.