Sen. Joni Ernst (R-Iowa) delivered the Republican response to President Obama's State of the Union address on Tuesday. (AP)

Sen. Joni Ernst (R-Iowa) has been in the Senate for only a few weeks, and while she has avoided the national spotlight so far, she is about to burst onto the scene via her designation as the Republican who will give the response to the president’s State of the Union address tonight. She hasn’t given her speech yet, but it is a given that the Democrats and their allies in the mainstream media will not like what she has to say. And it is my guess that they will not like Ernst either. Predictably, she will quickly be marginalized as a right-winger — or worse — by the usual suspects on the left. But Ernst proved during the 2014 campaign that she is an articulate, thoughtful, capable leader. So why will the Democrats despise her?

Joni Ernst speaks at an election night rally in West Des Moines, Iowa, last year. (Daniel Acker/Bloomberg News)

Well, by drawing on her uncommon, interesting personal story as an Iowa farmgirl and Army National Guard combat veteran, and relating to her fellow Iowans, Ernst captured one of the most reliably liberal Senate seats in the country — one that had been held by now-retired Democratic senator Tom Harkin for 30 years. While Ernst’s opponent ridiculed Sen. Chuck Grassley (R-Iowa) for being a farmer, Ernst embraced her roots and produced one of the most memorable, viral campaign ads of the 2014 cycle. Tonight, the “squealing” will begin.

But even more than losing a critical Senate seat, Democrats are frightened by Ernst because she is a woman who has a strong conservative philosophy and message that appeals to a lot of people. Democrats can’t dismiss Ernst as a token, because she didn’t run as one. Everything about her biography and style blunts the Democrats’ usual criticisms of conservative women.

Now when Hillary Clinton comes to visit Iowa, rather than having a friendly liberal trial lawyer senator by her side, she will be bracketed by Ernst — who no doubt will hold Clinton’s feet to the fire. It will be a woman-to-woman matchup, so the Democrats’ usual pablum about a GOP “war on women” just won’t work.

Generally, it doesn’t much matter who gives the State of the Union response. The half-life of whatever the opposing party has to say doesn’t even give the chosen speaker his or her 15 minutes of fame. But Ernst could be different. Expectations are high — but nothing about Ernst suggests that she isn’t up to the challenge. It is a big night for her, and a big night for the GOP.

From Sen. Marco Rubio (R-Fla.) to Gov. Bobby Jindal (R-La.), here's a look at some of the State of the Union rebuttals speeches from the 2000s. (Sandi Moynihan/The Washington Post)