ST. LOUIS (CN) – Russian hackers attempted to infiltrate U.S. Senator Claire McCaskill’s office network last year, the Missouri Democrat confirmed Thursday night.

At the time of the unsuccessful hacking attempt, McCaskill was just gearing up for one of the key re-election races in the 2018 midterm elections against Republican challenger Josh Hawley, Missouri’s attorney general.

Earlier this year, a poll showed McCaskill was 8 points behind Hawley, giving her the third-most precarious status among Democratic incumbents in the U.S. Senate this fall. Poll aggregator Real Clear Politics labels the race a toss-up. Missouri, a traditional Republican stronghold, gave President Donald Trump a 19-point victory in 2016.

The hacking attempt of McCaskill’s office email system was apparently unsuccessful. News of the attempted breach comes less than two weeks after special counsel Robert Mueller’s indictment of 12 Russian intelligence officers allegedly involved in the hacking of the Democratic National Committee during the 2016 election.

McCaskill confirmed the hacking attempt and blasted Russian President Vladimir Putin in a statement Thursday night.

“Russia continues to engage in cyber warfare against our democracy. I will continue to speak out and press to hold them accountable. While this attack was not successful, it is outrageous that they think they can get away with this. I will not be intimidated. I’ve said it before and I will say it again, Putin is a thug and a bully,” the two-term senator said.

The hackers reportedly used a technique called phishing to try to get McCaskill staffers to click on a link that would restore their expired Microsoft Exchange passwords. It is similar to a password-stealing technique used against Democrat Hillary Clinton’s presidential campaign chairman, John Podesta.

Microsoft found one of the phishing sites last fall and was able to determine who was targeted by the hack.

“We did discover that a fake Microsoft domain had been established as the landing page for phishing attacks, and we saw metadata that suggested those phishing attacks were being directed at three candidates who are all standing for elections in the midterm elections,” Tom Burt, Microsoft vice president for security and trust, said at a forum in Colorado last week, according to The Daily Beast. “We took down that domain, and working with the government were able to avoid anybody being infected by that particular attack.”

On Tuesday, President Trump was in Kansas City, Missouri, where he called Hawley on stage and called on voters to support his efforts to oust McCaskill in November’s general election, according to the St. Louis Post-Dispatch.

The audience booed when Trump mentioned McCaskill, criticizing her for voting against last year’s GOP-sponsored tax cuts.