Video (05:43) : Minnesota's lieutenant governor, a Democrat, will take over for Sen. Al Franken when he officially resigns from Senate.

Lt. Gov. Tina Smith accepted an appointment to the U.S. Senate on Wednesday, agreeing to replace Al Franken as one of Minnesota’s most high-profile elected officials and vowing to protect the seat for Democrats in next year’s special election.

“Though I never anticipated this moment, I am resolved to do everything I can to move Minnesota forward,” Smith said, moments after DFL Gov. Mark Dayton announced that she was his choice to replace Franken, who is resigning as a result of a sexual harassment scandal.

When she officially joins the Senate — likely to happen in early January — Smith will join Sen. Amy Klobuchar to make Minnesota one of only four states with two female senators (the others are California, Washington and New Hampshire).

In selecting Smith, Dayton chose one of his most trusted advisers, and someone who has spent the past few years traveling the state on his behalf, building relationships with influential DFLers and business leaders.

“First and foremost, I want to appoint the person who I believe will best represent the people of Minnesota in the United States Senate,” Dayton said at a Capitol news conference, with Smith at his side. He said Smith “will be a senator of whom all Minnesotans can be proud.”

The pick sets in motion a packed, high-stakes election cycle. For the first time in a generation, Minnesota voters in 2018 will select a new governor and two U.S. senators, with those races expected to cost tens of millions of dollars.

Gallery: Photo gallery: Tina Smith through the years Gallery: Photo gallery: Tina Smith through the years

Smith, 59, will have no time to waste. She must build a staff and adjust to the intricacies of the Senate and its polarized politics, where Democrats are trying to hold the line against President Donald Trump and GOP majorities in both houses.

Republicans immediately went on the attack.

The Minnesota Republican Party referred to Dayton’s choice of Smith as an “underhanded ‘House of Cards’-style move,” while the Republican National Committee said Smith has an “inclination for political ladder climbing and raising taxes on Minnesotans throughout her cushy insider career.”

“As a key player in the Dayton administration, Smith has tried to raise the gas tax and increase sales taxes on Twin Cities families,” said John Rouleau, executive director of the GOP-aligned Minnesota Jobs Coalition.

National and Minnesota anti-abortion groups will take particular interest in Smith, who a decade ago was vice president of public affairs for Planned Parenthood Minnesota, North Dakota, South Dakota.

“The choice of Ms. Smith is particularly egregious to Minnesota’s pro-life citizens, who will have no representation in the Senate,” Minnesota Citizens Concerned for Life, the state’s chief anti-abortion group, said in a statement. The group called Smith “an abortion industry insider.”

A number of Republicans are mulling a 2018 run, with party operatives and fundraisers most hopeful about the chances of former Gov. Tim Pawlenty, the last Republican to win a statewide race.

Smith’s remarks Wednesday had the makings of a 2018 stump speech, including a promise that she would be a “fierce advocate for economic opportunity and fairness.”

She talked about Minnesota’s strengths while nodding to its problems: “Minnesota has one of the lowest unemployment rates in the country, but I have heard stories from families who work two full-time jobs and still can’t find a good place to live.”

Jeff Blodgett, a longtime DFL operative who worked for the late Sen. Paul Wellstone, said he was “excited about the choice,” seeing Smith as someone who can carry the progressive baton.

Her commitment to running in 2018 may have helped the DFL clear the field of potential contenders. U.S. Rep. Keith Ellison, a Minneapolis progressive who could have mounted a serious challenge to Smith from the left, said Wednesday that he would take a pass on a Senate run.

Not having to compete in time-consuming and expensive DFL convention and primary campaigns would allow Smith to set her sights on the November election.

While she focuses on the 2018 campaign, Smith also enters a changing Senate landscape.

Democrat Doug Jones’ victory in Alabama Tuesday gives his party 49 votes to Republicans’ 51, turning every big vote in 2018 into a nail biter for the GOP. Franken still has not set a departure date, so it is unclear whether he or Smith will cast a vote against the contentious Republican tax bill.

Smith said she intends to move to Washington on Jan. 1, and added that the exact timing of Franken’s departure is not yet set.

“She’s in for a wild three years, assuming she wins” in 2018, said Jennifer Duffy, who studies the Senate for the Cook Political Report. “She’s got a pretty big hill to climb.”

DFL Gov. Mark Dayton on Wednesday appointed Lt. Gov. Tina Smith to the U.S. Senate, where she will replace Sen. Al Franken.

In those three years, Smith, who has never served in a legislative body before, will have to learn the Senate's arcane rules, carry out her legislative duties and mount an expensive campaign to win the seat to which she was appointed. She would then have to soon shift into campaign mode again to try to win a full, six-year term in 2020.

With Smith’s elevation, a Republican state senator is in line to become Minnesota’s new lieutenant governor — a strange set of political circumstances for Dayton’s last year in office. The current Senate president, Republican Sen. Michelle Fischbach of Paynesville, is set to become the new lieutenant governor under constitutional rules of succession. That in turn could trigger a state Senate opening with the potential to upset the GOP’s slim majority in that chamber.

For a time, Smith’s growing profile at the Capitol had led to speculation that she would run for governor. She decided not to join the field and to focus instead on closing out the final year of Dayton’s term.

Now, Smith finds herself in a Senate seat previously held by Wellstone, Walter Mondale, Eugene McCarthy and Hubert Humphrey.

The man she’ll succeed, Franken, released a brief statement praising Smith.

“She is a dedicated public servant who’s worked tirelessly on behalf of Minnesotans, and Gov. Dayton couldn’t have made a better choice for this job,” Franken said. “I look forward to working with her on ensuring a speedy and seamless transition.”

For her part, Smith thanked Franken for his service and said he’d been “a champion for our state.” Asked later about his decision to resign, Smith said it was “best for Minnesota.” She praised the women who have gone public with complaints against men in positions of power, saying they are at the leading edge of what she called “a sea change of attitudes” about sexual harassment.

“I think in some ways, this sea change is being led by young women, who tell women of my generation that maybe some of the things we put up with during our lives, we shouldn’t have to put up with,” Smith said.

Move up, not out ? Sen. Fisch­bach vows to handle two jobs, lieutenant governor and state senator. B1

Star Tribune staff writer Jennifer Brooks contributed to this report.