The mid-term elections that will take place in the U.S. on Tuesday are important for re-electing and electing new governors, lieutenant governors, attorney generals and state assembly and senate seats, but the U.S. Senate is where much of the concern is with vote watchers.

Will the Republicans win enough seats to take over the Senate while maintaining control of the House? How much will the lack of action on immigration reform be a factor in either encouraging or discouraging an outpouring of the Latino vote? Will the mid-terms be a litmus test for 2016? And will election voters see new demographic voting changing traditional red states into blue states or the reverse?

Certainly for Republicans to control the Senate, they need six seats. They are set to win three of those in Montana, South Dakota and West Virginia. The remaining three will depend on voter turnout and interest in Alaska, Arkansas, Colorado, Georgia, Iowa, Kansas, Louisiana, New Hampshire and North Carolina

Optimistic conservatives and GOP operatives say, yes, Tuesday will be a Republican wave of support. Polls show control of the Senate trending Republican. Democrats say no, like Vice President Joseph Biden.

"I don't agree with the odds makers. I predict we're going to -- we're going to keep the Senate," Biden told CNN's Gloria Borger on New Day in an exclusive interview on Monday.

"I ran for the Senate six times. And one of things I know about Senate races off years and on races, and on years, the same as governor's races, is it's all local. It all gets down to what the specific issues in that -- in that district or that state is. And each senator makes a judgment about whether or not it will be."

A new poll conducted by NBC News and The Wall Street Journal on Monday found voters favor Republican control of Congress by a single percentage point, 46 percent to 45 percent. The poll found only half of the voters said they were interested in the election.

State polls show Senate control is anybody's guess. A New Hampshire poll by WMUR and the University of New Hampshire gave Senator Jeanne Shaheen, the incumbent Democrat, a two-point lead over Scott Brown, the former Republican senator from Massachusetts.

A Quinnipiac University poll put the Iowa Senate race between Representative Bruce Braley, a Democrat, and State Senator Joni Ernst, a Republican, dead even, after a Des Moines Register poll showed Ernst pulling away by seven points just a day before.

In Colorado, Quinnipiac showed Representative Cory Gardner, a Republican, leading the incumbent Senator Mark Udall, a Democrat, by two percentage points, keeping that race too close to call.

Vice President Biden argued the mid-terms are decided by local issues for voters but Republican strategists think the lack of a national message has hampered them.

"I think one of the challenges of not having had a presidency for the last six years is it's very hard to develop a national message, and a larger platform that Republicans can run on," Kevin Madden, a Republican strategist, told The New York Times. "A lot of 2016 dynamic will be introduced on Wednesday after Election Day, and that will have a big impact on whether or not Republicans can offer a national agenda and a governing strategy."

In two key states, Georgia and Louisiana, a runoff (a second round of voting) is likely as there is no candidate capable of mustering more than 50 percent of the vote on Election day.

In Alaska, Senator Mark Begich, the incumbent Democrat, and Dan Sullivan, the Republican, are closely matched.

Early voting results do indicate that Democrats in some states, particularly in Iowa and North Carolina, are doing better than they did in 2010.

"Republicans are doing well. But the point is that Democrats aren't doing badly. They are hanging on in state after state, the polling suggests. And if they do better than just hang on, it will be because they will have brought voters to the polls on Tuesday who would otherwise never have show up," said John Podhoretz of the New York Post