Attack ads have fueled sharp ups and downs in the Alabama G.O.P. Senate race.

The three leaders of Alabama’s Republican Senate race have experienced giddy ascents and, in some cases, steep plunges, with the result that Representative Mo Brooks and two first-time candidates, Katie Britt and Mike Durant, enter Tuesday’s primary election tightly bunched together in recent polling. Unless one tops 50 percent, which seems unlikely, there will be a runoff between the top two.

One factor driving the ups and downs in the race is a flood of attack ads from deep-pocketed outside groups aligned with the candidates, which have spent freely to drive up negative impressions of their rivals. When voters say they aren’t swayed by TV ads, Alabama is Exhibit 1 that that is not the case.

Mr. Brooks, who jumped to a lead in the race last year and was endorsed by former President Donald J. Trump, was attacked by a super PAC that received $2 million from the Senate Leadership Fund, which is aligned with Senator Mitch McConnell. The Senate G.O.P. leader, who is often at odds with Mr. Trump for influence in the party, doesn’t want the hard-right Mr. Brooks to join his caucus next year.

An attack ad paid for by the super PAC funded partly by the McConnell group dredged up old clips of Mr. Brooks — a leader of Mr. Trump’s crusade to reverse the 2020 election — disparaging him in 2016. “I don’t think you can trust Donald Trump with anything he says,” Mr. Brooks said then.

During the time the ad was on the air, Mr. Brooks saw his support plunge to 16 percent in one poll. Shortly afterward, Mr. Trump withdrew his endorsement. Mr. Brooks has since regained a competitive footing, thanks in no small part to attack ads aimed at his two rivals.

Mr. Durant, a retired Army pilot who figured in the 1993 “Black Hawk Down” episode in Somalia, appeared to lead the race in the spring. But lately he has faltered, after being raked over the coals by a group calling itself Alabama RINO PAC, which is funded in part by the McConnell-aligned group. One ad, quoting without context remarks that Mr. Durant once delivered at the U.S. Army War College, includes him saying, “The first thing that needs to be done is to disarm the population.”

Another ad went after a supporter of Mr. Durant’s as “a top Never Trumper.”

The money behind both the anti-Brooks and anti-Durant ads comes from supporters, in state and out, of Ms. Britt, a former chief of staff of Senator Richard C. Shelby, whose retirement has opened the seat.

But Ms. Britt has hardly gotten off unscathed. The Club for Growth, the powerful anti-tax group based in Washington, which supports Mr. Brooks, is trying to undermine Ms. Britt. One ad says she is “really a lobbyist” because of a prior job leading a business group in Alabama; it goes on to quote a tweet from Donald Trump Jr. in 2021 — back when his father liked Mr. Brooks — calling her “the Alabama Liz Cheney.”

Many of the attacks seemed to have landed with voters, but also apparently confused them. There is no clear leader in the latest polls.