New York (CNN) New York federal prosecutors examining Rudy Giuliani's Ukranian business dealings are mindful of both the approaching 2020 presidential election and of the difficulty of prosecuting foreign lobbying violations as they move forward in their investigation, according to people familiar with the matter.

These people say charges against President Donald Trump's personal lawyer aren't certain or imminent, but that Giuliani has come into prosecutors' crosshairs as a central focus during the months-long inquiry.

In recent days, Giuliani has been in advanced discussions to hire Daniel L. Stein, a white-collar criminal defense attorney who is a veteran of the Manhattan US Attorney's office, to represent him in the investigation, sources say.

Prosecutors are examining possible financial crimes connected to Giuliani's Ukraine work, as well as possible foreign lobbying violations for those efforts. Giuliani is also the focus of a related counterintelligence inquiry

The Giuliani investigation is part of a broader inquiry that includes some of his associates. That probe began as early as February, but prosecutors delayed certain investigative steps until recently in an effort to avoid alerting people implicated in the probe and prevent it from becoming public.

On October 9, however, informed that some targets in the case were planning to leave the country, officials arrested and charged several of Giuliani's associates, including two who had introduced him to former and current Ukrainian officials as he searched for what he has said is damaging information connected to Trump's political rival, Democratic presidential contender Joe Biden.

Those two, Igor Fruman and Lev Parnas , and two co-defendants were indicted for allegedly funneling foreign money into US elections. All have pleaded not guilty.

Having been forced to bring the case unexpectedly, prosecutors worked at the office late into the night on the day the associates were arrested, and since have issued subpoenas and conducted multiple property searches of people connected to the alleged scheme.

According to the indictment, part of the campaign-finance scheme was designed to encourage a US congressman to pursue the ouster of the US ambassador in Kiev, Marie Yovanovitch. After Giuliani and other Trump allies complained that she stood in the way of Giuliani's investigative efforts in Ukraine, Trump removed her in May.

As prosecutors examine possible financial crimes connected to Giuliani's Ukraine work, they could consider a range of charges. They are also weighing possible foreign lobbying violations for those efforts, but they are cautious about bringing such lobbying charges, especially without other accompanying charges. That's in part because prosecutors in the Manhattan US Attorney's office are wary about the viability of cases concerning violations of what's known as the Foreign Agent Registrations Act after having observed how other recent cases have fared.

A spokesman for the US Attorney's office declined to comment.

Late last year, the New York office declined to bring charges of unregistered foreign lobbying against the former White House counsel under President Barack Obama, Greg Craig, CNN has reported. That case was eventually prosecuted by the DC US Attorney's office, and Craig was found not guilty in early September.

Prosecutors in New York monitored Craig's trial closely, according to people familiar with the matter, and when he was acquitted they felt vindicated by their decision to drop the case.

Later in September, a federal judge overturned the conviction of an associate of former Trump national security adviser Michael Flynn on similar charges.

In Giuliani's case, the investigation is still in its early stages and new information could inform their prosecutorial decisions.

In a pair of interviews with CNN last week, Giuliani said any work he did for foreign governments was only "for security purposes."

"I'm seeing that I'm being investigated for lobbying. I haven't done that. I see that I'm being investigated for representing a foreign government. I haven't done that," he said. "I've had a clause in my contracts since the Bush administration that I would not lobby or represent a foreign government."

He criticized the Manhattan US Attorney's Office, of which he was previously the head, saying it has acted improperly by failing to make him aware of its inquiry.

"Any neutral observer would say that if they're investigating me and haven't notified me, there is something wrong with that investigation. Not exactly a good faith investigation," Giuliani said.

As they pursue Giuliani, prosecutors are acutely aware of the need to consider the election cycle and next year's presidential contest.

In 2018, the year of the congressional midterm elections, the office charged two politically sensitive cases: one against Michael Cohen, Trump's former personal attorney, and another against Chris Collins, then a Republican congressman who was up for reelection that year.

The office charged both in August, around two-and-a-half months prior to the midterms, after weighing both the need to bring charges in a timely fashion and to avoid taking unnecessary steps that could influence an election.

Cohen pleaded guilty that August and is serving a prison sentence. Collins, who won his reelection while under indictment, ultimately pleaded guilty earlier this year and resigned his seat.