Cindy Hyde-Smith sworn in as Mississippi's latest senator
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Cindy Hyde-Smith (R) was sworn in on Monday to fill the seat vacated by former Sen. Thad CochranWilliam (Thad) Thad CochranTodd Young in talks about chairing Senate GOP campaign arm US farming cannot afford to continue to fall behind Mississippi Democrat drops Senate bid MORE (R-Miss.).  

Vice President Pence administered the oath on the Senate floor to Hyde-Smith, who was formerly Mississippi’s commissioner of Agriculture and Commerce.  

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Pence and Hyde-Smith are also expected to take part in a mock swearing-in from the old Senate chamber.

Hyde-Smith was appointed to the Senate seat after Cochran resigned on April 1 following four decades in the chamber.

Cochran announced his decision to retire last month, saying his health had became an "ongoing challenge" and he wanted to step down with enough time to ensure a "smooth transition" to his successor.

Cochran, who ran the Appropriations Committee, marked the third Senate committee chairman to announce his decision to retire or resign this year. GOP Sens. Bob CorkerRobert (Bob) Phillips CorkerGOP lambasts Trump over performance in Helsinki Flake to introduce resolution countering Trump's Russia summit rhetoric Corker: Trump made US look 'like a pushover' MORE (Tenn.) and Hatch, who oversee the Foreign Relations and Finance committees, respectively, are retiring after 2018.

Mississippi Gov. Phil Bryant (R) announced late last month that Hyde-Smith, a former Democrat who joined the GOP in 2010, would temporarily fill Cochran’s seat.

Hyde-Smith is the state’s first female senator and brings the total number of women in the Senate to 23 — an all-time high for the chamber.

Under Mississippi election law, a special election will be held in November for the remainder of Cochran’s term, which runs through 2020. If no one receives 50 percent of the vote, the top two candidates would then compete in a runoff.

Cochran’s retirement has shaken up Mississippi’s political scene.

Chris McDaniel, a conservative firebrand who unsuccessfully challenged Cochran in 2014, was running against Wicker in this year’s midterms but announced in March that he will run for Cochran’s seat instead.

Republicans are growing concerned that Cochran’s retirement could threaten their ability to keep his seat in the “R” column.

Hyde-Smith has close ties to the Trump administration and was reportedly considered for the role of Agriculture secretary after serving as a co-chair on President TrumpDonald John TrumpShocking summit with Putin caps off Trump’s turbulent Europe trip GOP lambasts Trump over performance in Helsinki Trump stuns the world at Putin summit MORE's Agriculture Advisory Committee during his presidential campaign.

But White House officials reportedly told Bryant that Trump would not endorse Hyde-Smith if she runs in November, fearing her past as a Democrat could be a ballot box liability.

Internal Republican polling showed Hyde-Smith behind both McDaniel and a Democratic candidate.