In a Saturday afternoon tweet, President Donald Trump accused Sen. Joe Donnelly, D-Ind., of "trying to steal the election" by paying for Facebook ads for Libertarian candidate Lucy Brenton.

The 2:05 p.m. tweet ended with a question: "Isn't that what Russia did?"

Donnelly is locked in a tight race with Republican Mike Braun, who Trump stumped for Friday at a rally in Southport. The president is scheduled to be back in Indiana on Monday to campaign with Braun in Fort Wayne.

Here's the full tweet:

"Rumor has it that Senator Joe Donnelly of Indiana is paying for Facebook ads for his so-called opponent on the libertarian ticket. Donnelly is trying to steal the election? Isn’t that what Russia did!?"

A spokesman for the Donnelly campaign said the ads were paid for by the Indiana Democratic Party, which earlier paid for a mailer urging fiscally conservative voters that Brenton is a better choice than Braun. He referred questions to the party.

Indiana Democratic Party Chairman John Zody released the following statement in response to President Trump’s tweet:

“The ads highlighting how Lucy Brenton is the true conservative in the Indiana Senate race are paid for by the Indiana Democratic Party. They are perfectly legal, factual, and accurately represent Lucy Brenton's anti-tax record. These ads draw attention to Rep. Braun’s record of voting to raise taxes on Hoosiers dozens of times as a State Representative while writing legislation to give himself tax breaks.”

Original story, Oct. 29, 2018: The Indiana Democratic Party sent out a mailer last week telling fiscally conservative Hoosiers there is a better Senate candidate than Republican Mike Braun.

But in an unconventional move, the flier, which says it was paid for by the Indiana Democratic Party, didn't suggest Hoosiers should vote for Democrat incumbent Sen. Joe Donnelly. Instead, the mailer praised Libertarian candidate Lucy Brenton.

The words "Looking for a candidate who will really lower your taxes?" appear on the front of the flier. On the back, the mailer says that Brenton "is an anti-tax conservative" while Braun "raised Indiana taxes 159 times." Donnelly isn't mentioned.

The idea of the ad: Die-hard Republicans likely won't vote for Donnelly. But conservative Hoosiers may find some common ground with Brenton.

More:Why final push by Braun, Donnelly could determine party control of U.S. Senate

More:Trump turns political at the national FFA convention

The Indiana Democratic Party did not respond to requests for comment.

Andy Downs, political science professor at Purdue University Fort Wayne, said the tactic is unusual — but it could actually pay off in the tight Senate race. Nearly every poll has shown Braun and Donnelly in a statistical tie.

And, in such a tight race, Brenton could be the "spoiler."

The most recent poll from CBS News shows 3 percent of 975 likely voters plan to vote for Brenton, compared to 43 percent who plan to vote for Donnelly and 46 percent who plan to vote for Braun. But previous polls have shown Brenton receiving up to 8 percent of the vote.

Some of those voters could still peel off and vote for Braun or Donnelly.

"The conventional wisdom is that Libertarians take votes away from Republican candidates. The idea being that the focus is on fiscal issues," Downs said. "However, Lucy Brenton has done well among folks who are traditionally Democratic voters as well."

Brenton said she was shocked that the Democrats used this tactic, but called the mailer "accurate."

"I am grateful for the free publicity highlighting my tax stance, but think it will backfire," Brenton said. "Many Democrats are Constitution loving, fiscally conservative voters and my message resonates with them, too. Ultimately, how well they targeted the addresses will determine which voters learn that they have a choice in this race that demands all of their freedoms, all of the time."

The Indiana Republican Party said the mailer was a "desperate, late-game campaign tactic."

"As we enter the final week before Election Day, it's clear that Democrats are desperate to win, and they'll do and say absolutely anything to beat Mike Braun -- including trying to trick Hoosiers," said Kyle Hupfer, chairman of the Indiana Republican Party.

Hupfer also highlighted Donnelly's own track record on taxes: he voted against President Donald Trump's tax reform plan.

Downs said the mailer was a risk, but one that was well calculated.

Donnelly's camp has taken other risks in recent weeks, including releasing video ads bashing the "radical left."

"A number of the polls have shown Brenton to be at a percentage that is higher than what we would expect for a Libertarian candidate," Downs said. "(Braun and Donnelly) are fighting over this group of voters, not just the undecided ones but the Brenton voters as well."

Call IndyStar reporter Kaitlin Lange at 317-432-9270. Follow her on Twitter: @kaitlin_lange.