Nóirín O’Sullivan has stepped down as Garda commissioner after 3½ years of incessant pressure. And now it really gets interesting.

Who will replace her? Who would want the job? And can anyone reform the Garda in one commissionership? Indeed, can anyone reform the Garda full stop?

When news broke that she was stepping down, there was relief in Government circles. But that will be short-lived.

To date, Taoiseach Leo Varadkar and Minister for Justice Charlie Flanagan, who are only in their jobs a few months, have been insulated from the difficulties and baggage of the O’Sullivan regime, which they inherited.

But that stops now. Her departure resets everything and the new commissioner will be seen as being of the Varadkar-Flanagan regime. They will now take the credit or the stick for the success or failure of Garda reform henceforth.

However, it is the Policing Authority to which responsibility falls to actually recruit the new commissioner.

Interviewed by The Irish Times earlier this year, authority chairwoman Josephine Feehily said the commissioner’s salary –just over €180,000 – would need to be increased to attract world-class applicants.

When Martin Callinan departed as Garda commissioner in March 2014, the government decided for the first time that an open competition would be held to fill the post.

An international headhunt was also conducted. But O’Sullivan, acting commissioner at the time, won the day and was awarded the job proper in November 2014.

Informed Department of Justice sources said she was far ahead of the other candidates in the race and easily emerged on top.

However, the same sources said there was disappointment that some very significant figures, including some who had been police chiefs abroad, had not applied for the job.

Garda sources believed there would be several candidates among the force’s most senior ranks interested in taking on the job. However, they believed that if a concerted, no-expense-spared effort were made to attract an international candidate, some internal candidates would be dissuaded.

The same sources believed somebody coming in from outside the Garda would face a huge challenge in familiarising themselves with Irish culture and policing.

“I think it might be embarrassing; that members might feel embarrassed,” said one Garda member. “You’d be admitting there was nobody already in the organisation capable of leading it. Do Irish people want that? I’m not sure.”

Other gardaí pointed to the public attitudes survey of last week, which reported satisfaction in the Garda above 70 per cent, as evidence that going outside the force for a new commissioner was not necessary.

At present it would be easy to lose track of the issues the new commissioner will face in terms of crisis management and long-term reform. The known crises include clarifying how many homicides slipped out of the Garda’s official crime statistics down the years.

There are also two new reports being conducted by Crowe Horwath for the Policing Authority on the fixed-charge notice system and the inflating of breath-test data.

The Garda last week published its two reports into these issues. And if Crowe Horwath finds any major shortcomings in the Garda reports or any new controversy lurking in the shadows, these matters will blow up again very quickly.

Not yet resolved, by a long way, are the financial governance shortcomings identified at the Garda College in Templemore.

The Garda’s audit section is conducting a final report into Templemore, and another audit into the alleged misuse of EU funding by the Garda is also under way.

The Commission on the Future of Policing in Ireland must also be dealt with.

And then there is the small matter of the Charleton tribunal, which is investigating allegations that a smear campaign was instigated against whistleblower Sgt Maurice McCabe. It is alleged that Martin Callinan directed that campaign and that O’Sullivan knew about it, at the very least.

With both of the former commissioners now gone, Charleton is set to spend millions of euro investigating two people who are no longer in the Garda and are outside the reach of any sanction.

O’Sullivan said in her resignation notice that her job had become an endless cycle of responding to queries and instructions from a host of Dáil committees, oversight bodies and other agencies of the State. Now the only part of that work she will be expected to continue is her engagement with Charleton.

Aside from all of the running controversies, the next commissioner will need to modernise and reform the Garda.

O’Sullivan had gathered up all of the recommendations from Garda Inspectorate reports down the years and had formulated a modernisation and reform programme based on them.

She had repeatedly claimed her implementation of that programme was well under way and would create a world-class police force.

The Policing Authority has been keeping under review the implementation of the programme, which covers everything from new crime investigation procedures to recruitment, civilianisation of more posts, new IT systems and much more.

Earlier this year, Feehily described O’Sullivan’s reform document as “huge”.

She said a lot of the reforms “haven’t been advanced with any kind of energy. There’s no point in being coy about that.”

It looks certain the reform programme will continue under the Deputy Commissioner, Dónall Ó Cualáin, who is now acting commissioner. But when the post is filled on a permanent basis, it is unclear whether O’Sullivan’s reform programme will be retained.

It is possible some form of slimmed-down programme would replace it; perhaps taking longer but with early and easy tangible wins prioritised at the start.

Both Government and Garda sources said it would be crucial that the Garda gets to grips, quickly and firmly, with crises as they arise. Many in the force believe problems have been allowed to fester for too long and have damaged the force unnecessarily.

One source said the drip-drip emergence of information in recent months about missing homicide cases was a case in point.

“Get a handle on it and get it all out publicly in one day and then move on,” he said. “You have problems dragging on at times for years, when months or even weeks should solve it. That has to stop – it’s killing us.”