The Wisconsin governor announced his decision a week before his state's primary.
In a speech in Wisconsin, Clinton put the future of the court at the center of the election debate.
The Wisconsin primary kicks off April's nominating contests.
"I do not make a habit out of supporting people who attack my wife and attack my family," Cruz said in an interview.
On Tuesday night, the GOP front-runner threatened to "spill the beans" on Ted Cruz's wife.
Arizona is the biggest prize for both parties Tuesday night.
Residents in three Western states are casting their picks as national security once again is a hot-button issue.
Twin explosions in Brussels will test how the contenders would protect the U.S. as president.
Trump needs to win around 55 percent of the remaining delegates to avoid a contested Republican convention in July.
An ex-model. A former NFL cheerleader. Stay-at-home moms. Even a former president.
Trump is busting ideological barriers. It's a political winner.
At a Wednesday town hall, the senator said he hypothetically wouldn't agree to the second-highest position in the U.S.
The Miami contest comes ahead of the crucial March 15 Florida primary.
The three White House wannabes would all likely face a skeptical, even hostile Congress. That means gridlock. Or mayhem.
It should not be assumed that denying Trump a first-ballot nomination means completely denying him the nomination.