Americans are preparing to vote in mid-term elections which will decide who controls the Senate and pave the way for the 2016 race for the White House.
Polling booths open on Tuesday beginning 06:00 Eastern (11:00 GMT).
The Republicans, who already control the House of Representatives, need to gain just six seats to take the Senate.
Meanwhile the Democrats are battling to stay ahead as President Barack Obama’s approval ratings fall to the lowest they have been since he was elected.
Many analysts predict a Republican victory as Obama’s popularity rate fails to climb much above 40%, despite recent improvements in the economy.
“This is a referendum on the president,” Republican senator and potential 2016 presidential candidate Rand Paul told NBC’s Meet the Press at the weekend.
But Democrats say their proven ability to rally their supporters ahead of elections could still give them the advantage.
“Grab everybody you know, get them out to vote, don’t stay home, don’t let somebody else choose your future for you,” Obama said during a campaign rally on Sunday.