GOP frontrunner Donald Trump took to Twitter Sunday morning to slam fellow GOP candidate Sen. Ted Cruz (R-TX) and Bob Vander Plaats, a social-conservative leader in Iowa who has endorsed Cruz.

Trump posted, “The Cruz campaign issued a dishonest and deceptive get out the vote ad calling voters “in violation.” They are now under investigation. Bad!”

He was referencing a mailer the Cruz campaign sent to Iowa voters has generated much criticism.

Then Trump moved on to call Vander Plaats a “phony.”

Trump then switched back to going after Cruz, attacking him for being born in Canada, and referencing a previous report about Cruz failing to disclose a loan from Goldman Sachs.

Trump and his wife attended church in Iowa Sunday morning before his two campaign rallies later in the day.