By Mark Simpson
Ireland correspondent, BBC News
The murder of soldiers at an Antrim army base leaves Northern Ireland's politicians and security chiefs with a major challenge.
Two were killed and four injured in the attack
The attack is part of an attempt by dissident republicans to wreck the peace process and bring down the power-sharing Stormont Assembly. Northern Ireland's authorities will be trying to find a way to ensure they do not succeed.
Now, the security focus is on Sir Hugh Orde, the chief Constable of the Police Service of Northern Ireland. He has been warning for months about the danger posed by dissident republicans and now we know why.
Clearly, he saw an intelligence picture showing an increase in the plotting and planning of attacks.
Sir Hugh applied but failed recently to get the job as the head of the Metropolitan Police. There will be many people glad now that he did not get the post as his experience in Northern Ireland will now be vital in the months ahead.
He warned earlier this week that the threat posed by dissident republicans was higher now than at any time since he became Chief Constable seven years ago. What happened in Antrim was exactly the sort of attack he was worried about.
In February 2009, a 250lb (114kg) bomb was defused close to an Army base in South Down. It was clear republican dissidents were stepping up their campaign.
Previously, their attacks had been erratic and sporadic, and aimed more at the police than the Army.
Unionists will be asking Sinn Fein why they criticised the police warnings about dissident republicans
It is worth pointing out that although the dissident factions are armed and extremely dangerous, they do not have the weaponry or the numbers of people to mount a sustained campaign like the IRA did during the Troubles. What is more, they have minimal public support.
They do not have a political wing which contests elections. They believe in the armalite not the ballot box.
Every politician in the 108-strong Stormont Assembly will condemn the Army base attack. However, that does not mean that all the parties will be speaking with one voice.
Unionists will be asking Sinn Fein why they criticised the police warnings about dissident republicans, and why they accused Sir Hugh of exaggerating the threat.
Appeals for help
What do Sinn Fein think now about those warnings?
It is a question which will have to be answered, and although in some ways it is a side issue, it illustrates the potential for the current security problem to escalate into a major political problem.
All sides will know that to jeopardise the power-sharing arrangements would be to give the bombers and gunmen what they want.
The truth is that the people of Northern Ireland had got used to relative peace
Nonetheless, the Sinn Fein criticism of Sir Hugh alarmed unionists, especially at a time when the parties are supposed to be working towards a local minister soon taking over policing and justice powers.
That is an argument for another day. The issue now is what to do to ensure the dissidents can never strike again?
Already there have been appeals for more public help for the police. At times like this, the police need all the help they can get, especially in hardline republican areas.
Security will be increased but don't expect to see troops back on the streets. The changes will be more subtle.
Suddenly, everyone who works for the police or Army will become more security-conscious.
For many people, it will bring back memories of the bad old days of the Troubles. The truth is that the people of Northern Ireland had got used to relative peace, and hoped that no-one would dare to try to wreck it.
That is why the First Minister Peter Robinson and Deputy First Minister Martin McGuinness were planning to be in the US next week on a coast-to-coast trip promoting Northern Ireland business.
That trip has now been delayed. The two men are staying at home to deal with the aftermath of the shootings.
It will be interesting to see whether the two leaders work together - and are seen together - in the coming days.
That will be a key indicator of how big a political problem has been created by the murders in Antrim.
For everyone involved in the new Northern Ireland, these are testing times.