The Spanish Supreme Court decision to jail the entire central committee of the Basque coalition Herri Batasuna (HB) for seven years is clearly a landmark. Whether it points to calmer waters, or to another upsurge in violence, is harder to make out.
The judges were clearly aware of the explosive potential of imprisoning the whole leadership of a legal political party. It may be the first time that this has happened in a European democracy.
Their careful judgment stresses that the 23 HB executive members are not being imprisoned because their political aspirations coincide with those of ETA, the Basque terrorist group. Their crime was the manner in which they attempted to publicise these aspirations.
In the 1996 general election, HB sought (unsuccessfully) to broadcast a video in which masked men put forward ETA's "Democratic Alternative". The judges held that the fact that these men had, quite literally, guns on the table indicated that the "alternative to the alternative" was further terrorist violence.
HB's attempt to broadcast these images therefore constituted "collaboration with an armed gang."
Yesterday HB lawyers announced that they would appeal to the Constitutional Court and, if necessary, to Strasbourg.
Mr Floren Aoiz, one of the convicted politicians, warned darkly of "direct and grave consequences", and called for a general strike.
The verdict and penalty have surprised some legal observers, who thought that HB's defence would gain an absolution or a token sentence.
The legal merits (or otherwise) of the judges' arguments are likely to be obscured by the political implications. The Spanish judiciary is theoretically independent, but in practice is subjected to very strong political and media pressure.
The prosecution was initiated under the outgoing Socialist government (PSOE), in the aftermath of two ETA killings. Mr Jose Maria Aznar's incoming Partido Popular (PP) has been keen to show that a conservative party is not afraid of a showdown with HB.
This was a popular stance with most of the Spanish public, and doubly so after one killing pitched anti-ETA sentiment far beyond any previous limits.
However, moderate Basque nationalists and some independent voices elsewhere have warned that the prosecution risks appearing to criminalise an entire political party and stimulating support for ETA.
As developments in recent months indicated that some people close to ETA were genuinely seeking an exit from the cul-de-sac of terrorism, it became evident that this trial could be a double-edged weapon. At first HB seemed to make things easy for the prosecution, rejecting bail when arrested and conforming to their stereotype as uncivilised radicals. When mass support for their cause failed to materialise on the streets of the Basque country, however, their thinking changed.
The erstwhile street agitators paid their bail, put on their ties, and put together a top-class legal team. Their intelligent, reasoned defence contrasted with a clumsy prosecution which had expected to be confronted with clenched fists rather than arguments.
Their court performance was such that it may have represented a de-facto move towards accepting the Spanish constitution. HB is a more complex social phenomenon than the tag "political wing of ETA" indicates. It has shifted back and forth between intransigent and relatively conciliatory positions.
Recent years have seen it radicalised, but the pendulum has swung back since the summer. The more moderate views represented by lawyers who masterminded the court defence seemed dominant.
The credibility of these people will be drastically undermined by the severity of the sentence. The response of ETA, and of HB's legions of street-fighting teenagers, will be awaited with anxiety.
The critical issue, however, is the make-up of HB's replacement leadership.
If the moderates - hammered, however inadvertently, by the Madrid judges - remain excluded from the new executive, the prospects for peace in the Basque country will recede yet again.
Three police officers were wounded when a bomb exploed in Spain's Basque region yesterday in the first apparent reprisal by ETA guerillas since the leaders of their political wing were jailed. Acting on a tip from an anonymous caller experts moved in to diffuse a bomb which exploded.