Senate Democrats do well, stay in the majority

Democrats gained at least one seat in the Senate by winning a series of high-profile races, giving them a continued stronghold in Washington and disappointing early Republican hopes of retaking the chamber.

Democrat Elizabeth Warren Tuesday after unseating Republican Sen. Scott Brown.

In one of the tightest races, Democratic Sen. Jon Tester of Montana won re-election over Rep. Denny Rehberg. That will give the Democrats at least 52 seats in the Senate, up from 51 currently. In addition, independent Sen. Bernie Sanders of Vermont, who caucuses with Democrats, won re-election, and in Maine, independent Angus King won a Senate seat held by retiring GOP Sen. Olympia Snowe. While Mr. King hasn’t said which side he would team up with in Washington, leaders of both parties expect him to join forces with Democrats, meaning the majority would grow to at least 54 seats, up from 53 currently.

The Senate race in North Dakota was the only one left undecided Wednesday. Democrat Heidi Heitkamp led Republican Rick Berg by 3,000 votes—a 50.5% to 49.5% edge— with all precincts reporting. Mr. Berg’s campaign said he wouldn’t concede until officials certified the result and left open the possibility that he would ask for a recount.

In the most closely watched contest Tuesday, Democrat Elizabeth Warren unseated Massachusetts Republican Sen. Scott Brown. And in Indiana, Democratic Rep. Joe Donnelly upset Richard Mourdock, who had defeated veteran Sen. Richard Lugar in a GOP primary.

In another marquee race, Rep. Todd Akin (R., Mo.), who ran into trouble after saying a woman’s body is capable of rejecting pregnancies in cases of “legitimate rape,” lost to incumbent Democratic Sen. Claire McCaskill.

In Virginia, Democrat Tim Kaine defeated a fellow former governor, George Allen, in a race that was close and hard-fought, with money pouring in from outside groups on all sides. That allowed Democrats to hold the seat of retiring Sen. Jim Webb in the swing state.

The losses by Messrs. Mourdock and Akin, in particular, are likely to prompt soul-searching within the Republican Party. In both Indiana and Missouri, GOP leaders were confident of victory until insurgent candidates backed by tea-party activists won their primaries, then proceeded to make controversial comments that helped Democrats to prevail.

That followed a similar pattern in 2010, when forceful conservatives won Senate nominations against establishment GOP candidates in Nevada, Delaware and Colorado, only to lose in the general election to Democrats whom Republicans considered to be beatable.

Some Republicans complain privately that GOP leaders have become too reluctant to give their backing to the party’s most electable candidates in primary elections, out of a fear of angering conservative activists.

Republicans did capture one Democratic-held seat in Nebraska, where Deb Fischer defeated former Sen. Bob Kerrey. Ms. Fischer will take the seat held by Democratic Sen. Ben Nelson, who is retiring. And in Nevada, the incumbent Republican, Sen. Dean Heller, fended off a challenge from Democratic Rep. Shelley Berkley in a tight race.

When the 2012 campaign began, Republicans believed they had good odds of retaking the Senate, since 23 Democrats were retiring or facing reelection, compared with 10 Republicans. But strong recruiting by Democrats, combined with the GOP missteps, bolstered the Democrats’ fortunes.

Mr. Mourdock stumbled when he said during a debate that when rape leads to pregnancy, “it is something that God intended to happen,” a comment that provoked an uproar. He said the next day that he stood by his position, but that “to twist and suggest that somehow God approves of rape is not what I was saying and certainly not what I intended.”

In Wisconsin, Rep. Tammy Baldwin, a Democrat, defeated the fourtime governor, Tommy Thompson. She will be the first openly gay senator in the nation’s history, on a night when Maine and Maryland became the first states to approve gay marriage in a popular vote.

At least 18 women—19 if Ms. Heitkamp wins in North Dakota— were set to take their seats in the Senate in the new year, a high water mark in the chamber.

Democratic Rep. Chris Murphy prevailed in Connecticut, thwarting a late charge by former wrestling-company executive Linda McMahon.

Democratic incumbents also held their seats in Florida, Ohio and Pennsylvania, as well as California, Delaware, Hawaii, Maryland, Michigan, Minnesota, New Jersey, New Mexico, New York, Rhode Island, Washington and West Virginia.

Republicans at one point or another hoped to mount strong challenges in the first three states on that list, but by the campaign’s end, the incumbent had a strong lead.

Massachusetts was a particular prize coveted by both sides. Ms. Warren, an outspoken critic of big banks and Wall Street, toppled a senator who became something of a GOP hero when he won the seat long held by the late Sen. Edward Kennedy.

Mr. Brown’s victory in early 2010 almost derailed President Barack Obama’s health-care law, and it was an early sign of the political shift that led to a GOP sweep in the 2010 congressional elections. But Mr. Obama has strong support in Massachusetts, and Mr. Brown’s personal popularity proved unable to overcome the state’s Democratic leanings during a presidential election year.

Most immediately, Senate Majority Leader Harry Reid (D., Nev.) will have a stronger hand during the lame-duck session of Congress beginning next week, with colleagues from both parties knowing he will keep his job when the new Congress takes office in January. Voters’ verdict on Tuesday night will hang over current lawmakers in the session as they try to head off automatic spending cuts and tax increases scheduled for January, the so-called fiscal cliff.

Next year, lawmakers of both parties hope to tackle a broad deficitcutting package that could include a tax overhaul, spending cuts and a revamping of safety-net programs like Medicare and Social Security.

Democrats hoped the defeat of Messrs. Akin and Mourdock, who are closely associated with the tea party, would make Republicans more willing to compromise on higher taxes for the wealthy. GOP leaders dismissed this, saying they were determined to oppose to higher taxes no matter what.