Republican presidential candidate Scott Walker responded sharply Monday night to a tweet from Hillary Clinton.
Earlier in the day, the Democratic frontrunner used the social media platform to accuse Walker of employing "bullying" tactics when dealing with unions.
"Unions help keep working families strong. Scott Walker's attacks on unions and workers' rights aren't leadership—they're bullying," Clinton wrote.
The tweet was signed with her initial, indicating she personally authored the tweet.
A few hours later, Walker responded — and hit back hard.
".@HillaryClinton Actually, we're protecting the American worker from being forced to support candidates like you," he tweeted.
This is not the first time Clinton has used Twitter to go after her GOP rivals. In August, Jeb Bush and Clinton faced off online over college tuition and taxes.