WASHINGTON (AP) -- Republicans made a final push Tuesday for at least six new Senate seats, banking on voter discontent with President Barack Obama to hand them the Senate majority for the first time in eight years.

Democrats hoped a strong voter-turnout operation would minimize their losses on an unfriendly campaign landscape. They were defending seats in seven states that Obama lost, several by landslide margins.

Senate Minority Leader Mitch McConnell of Ky. signs in at his poling station in Louisville, Ky., Tuesday, Nov. 4, 2014. (AP Photo/Timothy D. Easley)

Republicans, not content to stop there, hungrily eyed three other states - Colorado, Iowa and New Hampshire - where the president's once-solid popularity has sagged.

Democrats privately said they hoped to limit their net losses to five seats, which would barely keep them in control. But even that would require them to win several races Tuesday where they were struggling.

The GOP seemed certain to pick up three seats where Democratic senators are retiring: in West Virginia, South Dakota and Montana.

Republicans were bullish in Arkansas, where freshman Rep. Tom Cotton aimed to oust two-term Democratic Sen. Mark Pryor. They felt almost as optimistic about ousting Sen. Mary Landrieu in Louisiana - although a Dec. 6 runoff seemed likely. First-term Democratic Sen. Mark Begich of Alaska was another top target.

Victories in those six states would give Republicans the Senate majority, provided they don't lose any seats they now hold. Their biggest worries in that regard were in Georgia and Kansas.

In Georgia, where GOP Sen. Saxby Chambliss is retiring, Democrat Michelle Nunn and Republican David Perdue were locked in a tight battle.

In Kansas, three-term Republican Sen. Pat Roberts was scrambling to fend off independent candidate Greg Orman, who had persuaded the Democrat to leave the race and help him consolidate anti-Roberts sentiment. Orman hasn't said which party he will caucus with, however, so a Roberts loss doesn't automatically endanger the GOP's chances.

Kentucky's Senate race generated massive spending and national buzz. But Democrat Alison Lundergan Grimes' bid to upset Senate Minority Leader Mitch McConnell seemed to fade in the homestretch. Obama lost Kentucky by 23 points, and McConnell is a proven campaigner.

Elsewhere, contests for Democratic-held seats in three closely divided states could prove crucial.

In North Carolina, Democratic Sen. Kay Hagan is facing state House speaker Thom Tillis. The race set records for campaign spending, with airwaves drenched in political ads. Obama carried North Carolina in 2008, and lost it in 2012.

In Colorado, first-term Democratic Sen. Mark Udall faced a strong challenge from GOP Rep. Cory Gardner. In New Hampshire, Democrats said they believed Sen. Jeanne Shaheen could hold off Republican Scott Brown, a former senator from Massachusetts.

Few campaigns were as feisty and close as Iowa's, where long-time Democratic Sen. Tom Harkin is retiring.

Republican state Sen. Joni Ernst was facing Democratic U.S. Rep. Bruce Braley in a race that featured TV ads about castrating hogs, and a leaked fundraising video from Texas.

Barring a GOP wave, it's possible that control of the Senate won't be known for days or even weeks.

Slow vote counts in Alaska could make Republican Dan Sullivan's challenge against Begich too close to call for a while. In Louisiana, many expect a Dec. 6 runoff between Landrieu and GOP Rep. Bill Cassidy. And a Jan. 6 Georgia runoff between Perdue and Nunn also is possible.

If a runoff - or a vote recount in any closely contested state - will determine which party controls the Senate, the spending and politicking will be extraordinary.

A Republican takeover of the Senate would be huge politically, but its impact on governing is unclear. Even with Republicans controlling both houses of Congress, many of the dynamics that have fed federal gridlock for years would still be present.

Obama could veto legislation passed by a Republican-controlled Congress. And Senate Democrats, if relegated to the minority, could use the filibuster to thwart scores of GOP initiatives, just as Republicans have done to the Democrats for years.

A new Republican Senate majority could be short-lived. The 2016 Senate election map heavily favors Democrats, just as this year's map was ideal for Republicans.

In 2016, Republicans will be defending seats in seven states that Obama won, and in another three closely divided states. Most of the nine Democrats on the ballot will be solid favorites.

© 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Learn more about our Privacy Policy and Terms of Use.