Virginia Senate candidate Tim Kaine (D) suggested Thursday that he would be open to considering a minimum tax on Americans.

Kaine, the former governor of Virginia and former Democratic National Committee chairman, said during a debate versus Republican opponent George Allen that he would be open to a minimum tax proposal.

Evan Vucci / AP

Republican candidate George Allen, right, speaks as Democratic candidate Tim Kaine looks on during a Senatorial debate for the Virginia U.S. Senate seat on Thursday, Sept. 20, 2012 in McLean, Va.

"I would be open to a proposal that would have some minimum tax level for everyone," Kaine said when pressed by debate moderator David Gregory on whether Americans should face a minimum federal income tax. "But I do insist, many of the 47 percent that Gov. Romney was going after pay a higher percentage of their income in taxes than he does."

Kaine's remark came during a broader exchange about Republican presidential nominee Mitt Romney's comments that he couldn't count on about 47 percent of Americans to vote for him because they pay no income taxes and are "dependent" on government. Romney made those comments in May, which were surreptitiously recorded at the time and publicized this week.

Romney's controversial suggestion has become an issue in several competitive Senate races, such as Connecticut and Massachusetts, where Republicans Linda McMahon and Sen. Scott Brown have (respectively) distanced themselves from Romney.

Allen, the former Republican senator who lost his re-election bid in 2006, didn't as sharply distance himself from Romney. "I have my own view," he said about Romney's comments before pivoting to speak about jobs.

The Kaine-Allen race is one of the most competitive in the nation this year; its outcome could foretell control of the Senate in the next Congress. Republicans need to achieve a net gain of four seats to win back the majority in the Senate.

Last week's NBC News/Marist/Wall Street Journal poll of Virginia voters found the Senate race tied, at 46 percent apiece for Kaine and Allen.

Whether Kaine's comments today have any lasting effect will play out in the next days and weeks, though Republican observers of today's debate -- which was organized by NBC-Washington affiliate WRC -- immediately took note of the minimum tax comments.

While the presidential campaign remains the main event of the 2012 election season, a fierce, state-by-state battle is also underway to determine which party will control the U.S. Senate for the next two years.  And a series of NBC News/Wall Street Journal/Marist polls shows Democrats with an edge in two of the most closely-watched races and tied in a third.

In Ohio and Florida, the Democratic candidate holds a solid lead, while in Virginia – where former governor and onetime DNC chairman Tim Kaine faces former Republican Sen. George Allen in a marquee battle – the candidates are in a dead heat.

Republicans had entered the 2012 cycle with high hopes of winning all three races. All are seats currently held by Democrats, and winning any of them would advance the GOP toward the net gain of four seats they need to take back control of the Senate come January.

In Virginia, Kaine and Allen are deadlocked at 46 percent apiece with likely voters.

In Ohio, incumbent Democratic Sen. Sherrod Brown leads Republican State Treasurer Josh Mandel 49 percent to 42 percent.

And in Florida, two-term Democratic Sen. Bill Nelson, leads GOP Rep. Connie Mack 51 percent to 37 percent. Twelve percent of Florida voters said they were undecided about the race.

With only 54 days until the election, these three polls suggest that Republicans still have work to do if they wish to achieve their goal of retaking control of the Senate. Democrats must defend 23 of the 33 Senate seats on the ballot this fall, a numerical disadvantage that buoyed GOP hopes of reaching their goal early in the cycle, especially since many of the Democratic-held seats are also in hotly contested presidential battlegrounds.

President Barack Obama leads Republican presidential nominee Mitt Romney in Virginia, Ohio and Florida, according to the same NBC News/Wall Street Journal/Marist polls released Thursday.

Each of the Marist polls was conducted Sept. 9-11. Each poll has a 3.1 percent margin of error for its sample of likely voters.