Former Wyoming Rep. Cynthia Lummis Cynthia Marie LummisChamber of Commerce endorses McSally for reelection Cynthia Lummis wins GOP Senate primary in Wyoming Chamber of Commerce endorses Ernst for reelection MORE (R) on Thursday officially filed to run for outgoing Sen. Mike Enzi Michael (Mike) Bradley EnziChamber of Commerce endorses McSally for reelection Cynthia Lummis wins GOP Senate primary in Wyoming The Hill's Convention Report: Democrats gear up for Day Two of convention MORE’s (R-Wyo.) seat in 2020.

Lummis, a former member of the conservative House Freedom Caucus, previously represented the Equality State as the state's lone House representative, but opted not to seek reelection in 2016.

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Enzi, 75, in May announced his plans to retire from the upper chamber after serving 22 years.

Lummis is likely to face a difficult primary challenge, with many speculating House Republican Conference Chairwoman Liz Cheney Elizabeth (Liz) Lynn CheneyGOP lawmakers distance themselves from Trump comments on transfer of power Graham vows GOP will accept election results after Trump comments Liz Cheney promises peaceful transfer of power: 'Fundamental to the survival of our Republic' MORE (Wyo.) may opt to run for the position.

Former Wyoming Gov. Matt Mead, 57, has also been mentioned as a potential candidate in the race. Cheney, the No. 3 House Republican and the daughter of former Vice President Dick Cheney, previously sought to primary Enzi in 2014 before ultimately dropping her bid.

Lummis has not yet launched a campaign website or done media on her bid.

Bill Cubin, the treasurer of Lummis for Wyoming said despite the FEC filing to run, Lummis's camp said it doesn't constitute an official announcement.

"Cynthia will make an announcement regarding her plans in the near future. So, the news of the day, as far as Cynthia Lummis is concerned, is there is no news yet," he said in an email.

A GOP operative said to The Hill in a statement, “This looks like amateur hour. How do you file to run for office, without any campaign apparatus, but then claim you’re not actually a candidate?"

Sen. Rand Paul Randal (Rand) Howard PaulThe Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' Rand Paul says he can't judge 'guilt or innocence' in Breonna Taylor case Overnight Health Care: Health officials tell public to trust in science | Despair at CDC under Trump influence | A new vaccine phase 3 trial starts MORE (R-Ky.) encouraged Lummis — who previously endorsed him for president — to run for the position, two sources confirmed to The Hill.

Lummis, a former cattle rancher, was considered by the White House as a potential contender to serve as Interior secretary in 2017.

Updated at 4:36 p.m.