Vandals shattered a large window and spray-painted “ABOLISH ICE” early Tuesday morning at the Nebraska Republican Party offices in downtown Lincoln.
A newspaper carrier discovered the graffiti and damage to the building at 16th and N streets around 3 a.m., Officer Angela Sands said.
Lincoln police believe the vandals grabbed bricks from a nearby construction site and threw them at the window, she said.
Damage is estimated at $1,200.
Republican officials held a news conference at the site on Tuesday morning to condemn "this destructive criminal activity," suggesting it followed on the heels of "the increasingly radical rhetoric" of some national and state Democratic leaders.
Democratic State Chair Jane Kleeb said "we condemn the violence and vandalism that happened at the Nebraska Republican Party."
Pointing to the increasing intensity of current political debate, GOP state executive director Kenny Zoeller said "we need to dial this down."
"This is vandalism, not an act of free speech," Republican National Committeeman J.L. Spray said.
The incident and the news conference sparked a torrent of political reaction.
Gov. Pete Ricketts tweeted: "The vandalism of the @NEGOP headquarters by open borders activists is completely unacceptable. Nebraska Democrats must address the call to lawlessness in their party."
Meanwhile, Lincoln Mayor Chris Beutler said the act of vandalism "should be condemned by all" and he defended the Lincoln Police Department following a remark by Spray that Lincoln police have reacted to such vandalism with "a tepid response."
"J.L. Spray shouldn't be exploiting this issue to further divide us," Beutler said. "He should (be) using it (to) unite us behind the cause of political civility."
"Every criminal investigation deserves our best efforts and this incident is no different," Lincoln Police Chief Jeffrey Bliemeister said.
Zoeller said the GOP will install security cameras at its headquarters in response to the attack.
The vandals' red-painted "ABOLISH ICE" phrase refers to Immigration and Customs Enforcement, the federal agency that detains and deports people suspected of being in the country without permission.
Investigators are reviewing surveillance footage in the area to identify the culprits, Sands said.