Washington (CNN) -- Republicans are spending the final weekend of campaigning before Tuesday's election sizing up the possibility of their first Senate majority in nearly a decade, but with key races still too close to call.

Latest polls show some critical Senate races tightening, guaranteeing a night of drama and suspense on Tuesday, as Republicans strive for a net gain of six seats to capture the chamber. A GOP victory would give the party complete control on Capitol Hill and the ability to constrain President Barack Obama's final two years in office.

But the best the GOP can hope for is a slim majority, which would do little to end the era of gridlock and partisan division that has stifled Washington for years and contributed to an ugly public mood ahead of the election.

READ: How Mitch McConnell would run the Senate

Even if they win on Tuesday, there is no scenario in which Republicans will gain enough senators to build a 60 seat super-majority that is needed to move major legislation in a deeply partisan Congress.

Some races are so tight that turnout will be crucial. In Iowa, a CNN/ORC International poll had Republican Joni Ernst up by two points as she tries to grab a Senate seat held by the retiring Tom Harkin for nearly 30 years.

In North Carolina, Democratic Sen. Kay Hagan is clinging to a two-point margin in a state that leans Republican in another CNN survey.

In Kentucky, Sen. Mitch McConnell, the man in line to cap a long career on Capitol Hill by becoming Senate majority leader if Republicans win on Tuesday, appears to have opened a small gap over his Democratic challenger Alison Lundergan Grimes.

The GOP has a solid grip on the House and Republicans are expected to easily win Senate races in South Dakota, Montana and West Virginia.

Other battlegrounds are in Alaska, Arkansas, Louisiana, New Hampshire, Georgia and Colorado.

READ: Poll: Republican Ernst has small lead in tight Iowa Senate race

Top party surrogates and potential 2016 presidential candidates were fanning out in battleground states with three days to go.

Hillary Clinton appeared with Grimes in Kentucky, and pleaded with voters not to heed "fear" tactics from Republicans she called the "guardians of gridlock."

"Don't wake up the day after the election wishing you had done just a little more," Clinton told Grimes supporters. On Sunday, Clinton will take her turnout machine to New Hampshire to support Sen. Jeanne Shaheen who is in a surprisingly close tussle with challenger Scott Brown.

Her husband, Bill Clinton meanwhile tried to give Democrat Bruce Braley a boost in Iowa on Saturday.

New Jersey Governor Chris Christie was headlining a rally in Ohio for Republican Governor John Kasich, who is seeking re-election. Obama, who has been a drag on Democratic candidates, was nevertheless headed to Michigan on Saturday to campaign for Senate candidate Gary Peters and Representative Mark Schauer.

Georgia will meanwhile on Sunday hold the final debate before election day of a compelling race between Michelle Nunn and Republican David Perdue, in which Democrats are hopeful of pulling off a shock win.

Two Senate races, in Louisiana and Georgia could trigger run-off elections, so it is possible the fate of the chamber will be in limbo for weeks.

READ: Poll: Hagan holds slim lead in North Carolina Senate race