Ernst, a lieutenant colonel in Iowa's national guard and first-term state lawmaker, has received encouragement from Iowa Gov. Terry Branstad (R) and Lieutenant Gov. Kim Reynolds (R) to run for the seat.

She joins an already-crowded field of fairly unknown GOP candidates, after all of the state's well-known Republicans took a pass on the race. Declared candidates include David Young (R), who until recently was Sen. Chuck GrassleyChuck GrassleySenate locks in hate crimes deal, setting up Thursday passage Conservative House members call on Senate to oppose ATF nominee House votes to extend ban on fentanyl-like substances MORE's (R-Iowa) chief of staff, as well as former U.S. Attorney Matt Whitaker (R) and conservative radio host Sam Clovis (R). Businessman Mark Jacobs (R) is also looking at a run.

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The eventual primary winner will go on to face Rep. Bruce BraleyBruce Lowell BraleyThe Memo: Trump attacks on Harris risk backfiring 2020 caucuses pose biggest challenge yet for Iowa's top pollster OPINION | Tax reform, not Trump-McConnell feuds, will make 2018 a win for GOP MORE (D-Iowa), who Democrats have rallied around as their standard-bearer. Braley already has more than $2 million in the bank for the race after raising more than $1.25 million in the last three months.

A survey released Wednesday by the Democratic firm Public Policy Polling shows Braley leading his GOP opponents by 9-3 points, though much of that lead may be due to their relative anonymity in the state.