Republican presidential Ted Cruz Rafael (Ted) Edward CruzSenate Republicans face tough decision on replacing Ginsburg Cruz: Trump should nominate a Supreme Court justice next week Renewed focus on Trump's Supreme Court list after Ginsburg's death MORE mocked Donald Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE for threatening to skip Tuesday night's presidential town hall and continued to challenge the GOP presidential front-runner to a one-on-one debate.

Cruz held a rally in Brookfield, Wis., following Gov. Scott Walker’s (R) endorsement of the Texas senator one week ahead of the state’s primary. The former presidential hopeful called Cruz "a principled constitutional conservative who can win."

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Cruz noted that "it’s neck and neck. Donald Trump and I are effectively tied in the state of Wisconsin. That means ... any candidate running for president owes it to come in front of the state and actually debate.

"Now our friend Donald finds debates very, very stressful," Cruz continued. "They make his hair stand on end."

Cruz has repeatedly called on Trump to debate him as the GOP field continues to winnow.

The GOP presidential candidates are scheduled to participate in a CNN town hall on Tuesday night. Cruz has suggested combining the separate interviews into a Trump-Cruz debate.

On Tuesday morning, Trump threatened to skip the network's town hall and accused CNN reporters of treating him unfairly.

"We’re in the same location. They got the TV cameras; they got the moderators ... the one thing they’re missing is The Donald," Cruz said.

"Donald prefers to communicate in 140 characters or less," he said.

"The people of Wisconsin deserve a real debate," Cruz added. "Donald’s absence speaks even louder than his presence."

Cruz and Trump are in a tight race in the Badger State as the Texas senator seeks to close the gap in delegates.

Cruz leads by less than a point in Wisconsin, according to RealClearPolitics.