NASHVILLE (AP) - A new poll by Middle Tennessee State University indicates Gov. Bill Haslam and fellow Republican U.S. Sen. Lamar Alexander hold wide leads over their Democratic challengers, but that support for the incumbents hovered around or below 50 percent.

The poll showed that 51 percent of likely voters planned to cast their ballots for Haslam, while only 18 percent planned to vote for Democrat Charlie Brown. The remaining 30 percent were undecided, planned to vote for someone else or refused to say.

Meanwhile, 44 percent of likely voters said they plan to vote for Alexander, compared with 26 percent for Democrat Gordon Ball.

Previous MTSU polling showed Haslam's popularity dropped from 61 percent 47 percent between the spring of 2013 and 2014, while Alexander's popularity dropped from 54 percent to 43 percent.

The poll also found a proposed constitutional amendment to ban a state income tax could face a tough time being ratified on Tuesday.

A low level of voter participation could sink the proposed amendment, as efforts to change the constriction must gain a majority of the number of people voting in the governor's race to be ratified.

The MTSU pollsters surveyed 600 registered voters, and the results have a margin of error of plus or minus 4 percentage points.