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Carlos Osorio, Associated Press
Former Massachusetts Gov. and 2012 Republican presidential candidate Mitt Romney campaigns for Michigan Senate candidate Terri Lynn Land during a rally in Livonia, Mich., Thursday, Oct. 2, 2014.

DES MOINES, Iowa — Mitt Romney was visiting Iowa Sunday to campaign for U.S. Senate candidate Joni Ernst, one of several Republicans in battleground states hoping to capitalize on President Barack Obama's sagging approval rating two years after he defeated the former Massachusetts governor to win a second term.

Romney, the 2012 GOP nominee, was to headline an event Sunday evening in West Des Moines with Ernst, a state senator who is locked in a tight race with Democratic U.S. Rep. Bruce Braley.

Romney's visit, which includes a stop with Ernst Monday in Cedar Rapids, is part of the Massachusetts governor's role a senior leader in a national Republican Party in search of one. Since the 2012 election, his national popularity has improved, as Obama's has foundered amid the economy's slow recovery and international crises.

And unlike the president, Romney has been busy in the past two weeks making public appearances on behalf of Republicans in competitive Senate races. Republicans need to gain six seats in the Nov. 4 elections to claim the majority.

"Incompetence in Washington is really holding back America," Ernst said in a statement. "Mitt cares deeply about the future of our nation."

For Democrats, first lady Michelle Obama has been a more popular draw. She campaigned in Des Moines for Braley on Friday. Braley was scheduled to knock on doors with campaign volunteers in his home area of northeast Iowa Sunday.

"I was so thrilled to share the stage with the first lady," Braley said in a press statement Friday. "She knows how important our race is."

Romney's schedule has included stops in Michigan, Kentucky, Georgia, Colorado and Iowa. The latter two are the only close Senate battles in states where Obama beat Romney but where a Democratic Senate seat is in jeopardy.

In Colorado, Sen. Mark Udall is facing a stiff re-election challenge from U.S. Rep. Cory Gardner, while Braley and Ernst were in a dead heat for the seat held by retiring Democratic Sen. Tom Harkin. A Des Moines Register/Bloomberg Politics Iowa Poll published Saturday showed Ernst holding a 48 to 47 percent lead over Braley, marking improvements in the past two weeks by both candidates though more by Braley.

Meanwhile, Obama's job approval was 39 percent in Iowa, where he won by five percentage points in 2012 but where voters say today they would prefer Romney, according to the new Iowa poll. The poll taken last week included responses from 1,000 likely voters in Iowa, and had a margin of error of plus or minus 3.1 percentage points.

Romney is well known among Iowa Republicans having competed in the state's leadoff presidential caucuses in 2008 and 20012. He finished in second place both times.