Washington (CNN) Election officials in Indiana have concluded that former Sen. Evan Bayh is an "inactive" voter in their state after they failed to confirm he lives in Indianapolis, creating a new problem for the Democrat as he mounts a late effort to win back his old Senate seat.

According to records obtained by CNN, Bayh has been listed as an inactive voter twice since leaving office -- once in July 2014 and the second time last week.

In both instances, election officials had sent multiple postcards to Bayh's Indianapolis address to determine that he lives there. Both times the post office could not reach Bayh at the condo he owns in Indianapolis despite multiple attempts, prompting the Indiana Election Division to list him as inactive, according to copies of the mailers and state voting records.

Bayh is still a registered voter, and being listed as inactive does not prevent the former two-term senator and governor from voting in the state. But being considered inactive is the first step from being removed altogether from the voter rolls.

Bayh has voted by absentee ballots in Indiana elections since leaving office, requesting those ballots be sent to his home and office addresses in Washington, the records show. (He voted in person in May, his office said.)

Perhaps more significantly, the inactive designation is only bound to intensify GOP accusations that the former senator had swiftly abandoned his state for Washington in his nearly six years since leaving office, only to come back to Indiana last month in a last-ditch effort to return to power.

The new revelations come just days aftear a CNN report showed Bayh consistently listing his two multi-million-dollar homes in Washington as his main places of residence, not his $53,000 condo in Indianapolis, contradicting his public claims that he "never left" the state after giving up his seat in 2011.

It is similar to the problems that dogged former Sen. Richard Lugar, the veteran Indiana Republican who lost his 2012 primary after he was sharply criticized for not owning a home in Indiana and for living in the Washington suburbs instead.

On Thursday, Bayh's campaign did not dispute the "inactive" status but downplayed the significance, noting that he still votes in Indiana elections and hundreds of thousands of other voters have also been listed as inactive.

But the Democrats argued that Republicans have been engaged in a long-running effort to discredit Bayh's ties to Indiana with little success -- dating back to 1988 when Republicans challenged Bayh's eligibility to run for governor of Indiana, only to be rejected by the Indiana Supreme Court. Bayh's aides accused their GOP opponent, Rep. Todd Young, of playing dirty tricks.

"Congressman Young's party bosses realized as far back as 1988 that the only way they can beat Evan Bayh is to take the choice away from voters, and they've been trying and failing to do that ever since," said Bayh spokesman Ben Ray. "This latest attempt to make a mountain out of a molehill -- from a bunch of folks that couldn't count to 500 to get their congressman on the ballot, no less -- is the definition of something a losing campaign does."

Bayh's office was referring to problems earlier this year that hounded Young over whether he obtained the requisite number of signatures to get onto the ballot.

Young campaign officials declined to comment.

Election officials couldn't determine Bayh residency

To clean up its voter lists, Indiana sends out postcards every two years to registered voters in the state. If the postcards bounce back twice, voters are listed as "inactive," according to state election rules. They are considered "active" again once they cast their vote.

In 2014, the state determined that there were 696,000 voters such as Bayh who were listed as inactive out of 4.4 million postcards sent, according to Valerie Warycha, a spokeswoman for the Indiana secretary of state's office.

Most of the inactive voters are either dead, in prison are no longer living at their address, Warycha said. She said that 2014 was the first time in years that the state had tried to determine voter activity on a statewide level. Bayh was listed as inactive on July 18, 2014, but he was put back in "active" status in December of that year after he voted by absentee ballot that November.

"The whole point of the project is to make sure people actually live at that address," Warycha said.

In 2016, Bayh appeared to have been forwarding his mail at his Indianapolis condo to Washington. But the state does not allow the voter-related postcards to be forwarded to a different address because they are trying to establish Indiana residency, according to election officials. Earlier this year, the first postcard was not deliverable to Bayh's address, with the post office stamp noting "unable to forward." He was listed as "inactive" on August 10, records show.

For his part, Young is listed as an "active" voter, though one voter-related postcard sent to his Bloomington address was bounced back earlier this year. (A Young official said it was because the congressman moved and the postcard was sent to his old address. It was updated in the system, the official said.)

Bayh in the lead, but under scrutiny

Bayh, 60, is still the favorite in the race against Young, up 7 points in a new Monmouth University poll . His reputation as a centrist politician, along with the fondness of his family name and his long-time service as a senator and governor, make him a serious contender in a race that could determine control of the Senate majority.

But Republicans have new hope that they could use his post-Senate life against him.

Bayh's decision to run again for office surprised many people in Washington because he had sharply criticized the Senate as a feckless institution when he left office. And he had a successful career after leaving, signing on a senior adviser to a private equity firm, Apollo Global Management, and a strategic adviser with the downtown Washington firm, McGuireWoods. He also served on five corporate boards, was a paid analyst with Fox News and became a paid speaker.

His speaking firm, Leading Authorities, noted on its website that he travels "from D.C."