ALBANY, New York (CNN) -- Aides to crime-fighting New York Governor Eliot Spitzer and the state's lieutenant governor have begun planning for a possible transition after federal prosecutors linked Spitzer to a high-end prostitution ring, a top legislative staffer said Tuesday.
Elliot Spitzer was a political ally of presidential candidate Hillary Clinton.
On Tuesday evening, a Spitzer spokesperson said he had made no decision on his political future yet.
Sources knowledgeable about the investigation said Tuesday that Spitzer, the key ally of Democratic presidential candidate Hillary Clinton, spent more than $15,000 dollars for several encounters with prostitutes.
The Republican leader of the state Assembly said he would move to impeach Spitzer if he remained in office.
Spitzer built his career on rooting out public corruption as New York attorney general, and became a national figure with a series of high-profile Wall Street investigations.
He is also known for prosecuting prostitution rings and earned the tabloid nickname 'Eliot Ness' after the incorruptible hero of "The Untouchables." Read Todd Benjamin's blog
Spitzer apologized publicly to his family and the people of New York on Monday but did not elaborate on the scandal.
At a hastily convened news conference in Albany, the state capital, he confessed to an undisclosed personal indiscretion, saying he had acted "in a way that violates my obligations to my family."
Watch as Spitzer faces calls to quit »
Once seen as a rising star in the Democratic party, Spitzer took office in January 2007 with a landslide victory after serving eight years as the state's attorney general. But the scandal raises questions about whether he will make it through a second year.
A Democratic source with firsthand knowledge of the issue said: "It is a 'when' question on the resignation. Not an 'if'... Eliot knows he cannot hold onto his job here."
Another Democratic campaign veteran with ties to the Spitzer team said: "The political people were clear about the options. There are none. Not for him."
"I think there's no question if he is involved -- and I'm not saying he is, because we don't know all the facts -- I would say he'd have to resign," said James Tedisco, the Republican minority leader in the state Assembly.
Tedisco said Spitzer's push to reform government "loses all validity if he was involved in something illegal like that." 
See a timeline of his life »
The Republican Governors Association called on Spitzer to resign to "allow the people of New York to pursue honest leadership."
If Spitzer were to resign, Lt. Gov. David Paterson would become New York's first African-American governor.
Hillary Clinton sidestepped questions about the sex scandal threatening her home state governor and political ally.
"I don't have any comment on that," she said when asked about the allegations. "Obviously, I am sending my best wishes and thoughts to the governor and to his family," Clinton said.
The allegations, revealed Monday in The New York Times, were outlined in federal court papers detailing a meeting in a Washington hotel room last month between a prostitute and a client who a source told CNN was Spitzer.
A source familiar with the investigation identified as the hotel as the posh Mayflower Hotel. Sources said Spitzer rented two rooms -- one under the name of a political donor.
The affidavit does not mention Spitzer by name, but a source with knowledge of the case said the subject identified as Client-9 is the governor. He has not been charged.
His alleged involvement with the ring was caught on a federal wiretap, the source said.
• Time magazine names Spitzer "Crusader of the Year" during his two terms as New York attorney general.
• Tabloids label him "Eliot Ness," because of his reputation for rooting out corruption, busting white-collar criminals and tackling organized crime.
• Spitzer is known for prosecuting several prostitution rings.
• He attended Princeton and Harvard, then became an assistant district attorney in Manhattan.
• He worked for three New York law firms and decided to run in his mid-30s for attorney general.
• The first-term Democrat had been considered a rising star in his party.
• Spitzer is married and has three daughters.
The prostitute, identified only as "Kristen" worked for the Emperors Club, which charged between $1,000 and $5,500 an hour and operated in New York; Los Angeles, California; Miami, Florida; London, England; and Paris, France, according to court papers.
According to the affidavit, defendant Temeka Rachelle Lewis -- who is accused of working as a booking agent for the club -- wrote a text message Monday, February 11, asking the operation's day-to-day organizer to "pls let me know if (Client-9's) 'package' arrives 2mrw. Appt wd be on Wed." Prosecutors say the message was a reference to a deposit.
On Tuesday, according to the affidavit, Lewis sent a message to Kristen, saying Client-9's deposit had not arrived but she should be able to "do the trip" if it arrived the next day. View a gallery of recent political sex scandals »
In a later conversation, Lewis and Kristen discussed when the prostitute could take a train from New York's Penn Station to Washington's Union Station, the affidavit says. Client-9 would be "paying for everything -- train tickets, cab fare from the hotel and back, mini bar or room service, travel time, and hotel."
The affidavit says that, about 5 p.m. Tuesday, February 12, Lewis spoke with Client-9 on the telephone and told him that his "package arrived today." The client asked Lewis whom he would be meeting and, when told it was Kristen, said, "Great, OK, wonderful."
The two discussed how the woman would get a key to his room for a Wednesday rendezvous and how they could arrange credit for future services.
"Client-9 asked Lewis to remind him what Kristen looked like and Lewis said that she was an American, petite, very pretty brunette, 5 feet 5 inches and 105 pounds," the affidavit reads.
In a call to Lewis, Client-9 was told the balance would be $2,712.41, but Lewis suggested he give Kristen $1,500 or $2,000 more so that he would have a credit.
According to the affidavit, Kristen called Lewis about 9:32 p.m. Wednesday, February 13, and told her she was in Client-9's room -- No. 871 -- at the Washington hotel.
Four minutes later, Client-9 was in the hotel, Lewis told Kristen in another call.
No more calls were logged until 12:02 a.m. Thursday -- Valentine's Day -- nearly 2½ hours later. At that time, Kristen told Lewis Client-9 had left and she had collected $4,300.
Lewis told the prostitute she'd been told that Client-9 "would ask you to do things that, like, you might not think are safe -- you know -- I mean that ... very basic things," the affidavit says. E-mail to a friend 
CNN's Kelli Arena, John King, Kevin Bohn and Dana Garrett contributed to this report
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