Originally Published: 24 SEP 21 06:20 ET

Updated: 24 SEP 21 13:39 ET

By Chandelis Duster and Karl de Vries, CNN

(CNN) -- Iowa Republican Sen. Chuck Grassley announced on Friday that he will run for reelection, further solidifying Republican chances of holding the seat in 2022.

"It's 4 a.m. in Iowa so I'm running. I do that 6 days a week. Before I start the day I want you to know what Barbara and I have decided," Grassley, who is 88 and was first elected to the US Senate in 1980, wrote on Twitter, including a GIF of himself running. "I'm running for re-election—a lot more to do, for Iowa. We ask and will work for your support. Will you join us?"

Grassley's announcement ends months-long speculation over whether he would run. Former Iowa Rep. Abby Finkenauer is the highest-profile Democrat to so far announce a challenge for the seat, though Iowa has trended more conservative in recent years and backed Donald Trump in both 2016 and 2020.

"After 47 years in Washington, D.C., Chuck Grassley has changed from an Iowa farmer to just another coastal elite," Finkenauer said in a statement after Grassley's announcement, accusing him of "running yet again on an agenda that puts big pharma over our seniors, Wall Street over workers, and monopoly corporations over the mom and pop small businesses that make Iowa strong."

Grassley leads Finkenauer 55% to 37% among likely voters in a Des Moines Register/Mediacom Iowa poll taken earlier this month. Another 7% are not sure who they would vote for in a head-to-head matchup, and 1% would not vote.

Grassley in the past has dismissed polls suggesting many of his constituents want him to step aside and said last week that he's hearing "a lot of encouragement" from Iowans to run again. He said he had planned to have his decision made by November 1, but added: "I'm thinking about doing it sooner."

"I've been getting a lot of encouragement from Iowans for the first time -- they haven't talked to me much about it until now," Grassley previously told CNN. "I think I keep the same schedule as when I was 65 years old, maybe even 40 years old," he said with a laugh.

Grassley, the 10th longest-serving US senator in history, is the top Republican on the Senate Judiciary Committee and holds several influential committee spots.

This story has been updated with additional background information.