President Barack Obama said on Tuesday that the Senate electoral map heavily favors Republicans, making it the toughest grouping of races faced by a second-term president since Republican Dwight Eisenhower lost heavily in 1958.

Obama, who called a local radio show in Hartford, Connecticut to encourage people to vote, noted that only a third of the Senate seats are up for election, and that this cycle, those races are in Republican-leaning states.

"In this election cycle, this is probably the worst possible group of states for Democrats since Dwight Eisenhower. There are a lot of states that are being contested where they just tend to tilt Republican," Obama said on WNPR.

In 1958, Democrats took 13 Senate seats, including 10 from Republican incumbents, and won both Senate seats in the first-ever Senate election for Alaska.

The White House is fighting back against assertions that Tuesday's midterms are a referendum on Obama's performance. Republicans are expected to pick up seats in the Senate and may gain the six they need to wrest control of the chamber from Democrats.

Obama did 14 interviews with local radio stations on Monday and Tuesday leading up to the midterms, including in Milwaukee, Philadelphia, Miami, Baltimore, Chicago, Charlotte, and Detroit.

Obama was calling the Hartford radio show to express his support for Connecticut Governor Dan Malloy, who is in a tight race with Republican challenger Tom Foley.

Of the 36 gubernatorial races, more than a dozen are considered too close to call.

"That probably speaks to the fact that voters are generally frustrated with government," Obama said.

"They know things have gotten better from where they were six years ago, but they don't see the kind of cooperation between Democrats and Republicans they'd like to see. The polarization has gotten worse," he said.