When he burst on to television screens across the world last week, speaking perfect English, President Saakashvili looked every inch the charismatic New York-trained lawyer that he is.

Known to friends as “Misha” the cosmopolitan 40-year-old is unquestionably brilliant, speaks half a dozen languages, and has a Dutch wife he met in Paris. But Mr. Saakashvili has handed Russia a victory it could scarcely have dreamed of — his decision to invade South Ossetia has left his army humiliated and he could soon be fighting for his political life with no prospect of any meaningful help from his Western allies.

How did he make such a catastrophic blunder?

The answer appears to lie in Mr. Saakashvili’s own character. While supporters praise him as a passionate and patriotic leader, whose drive and energy have transformed Georgia, critics say he is bombastic, impulsive, and confrontational and his suave exterior hides a burning nationalist pride.

His abject defeat will hurt further still because it means the loss of a long personal battle with Prime Minister Putin.

A few years ago, a document titled “Mikheil Saakashvili: A Psychological Study,” origin unknown, was circulated among Western journalists.

The now discredited paper claimed Mr. Saakashvili’s behavior was narcissistic, paranoid, egocentric, and hysterical and showed “psychiatric disturbances.”

There is no doubt that Russia has been trying to undermine Mr. Saakashvili for years.

According to diplomatic sources, Russia stepped up its campaign to provoke him into a rash move in South Ossetia or Abkhazia — the two breakaway provinces of Georgia — over the past two weeks. There were occasional clashes and Russian jets entered Georgian airspace.

Mr. Putin, it seems, knew just which buttons to push and Mr. Saakashvili took the bait.

Friends of Mr. Saakashvili claim he is neither a nationalist hothead, nor a political ingenu, and has instead simply been naive.

An expert on the region who taught the Georgian president at Columbia University in the 1990s, Scott Horton, said: “He’s not a hothead, that’s Russian propaganda. That’s the way they would like to see him portrayed in the West.

“But I think it was a mistake for him to act as he did and the better policy would have been to show restraint. Did he make a tactical blunder? The answer is almost certainly yes, but I don’t think it was more than a tactical blunder.

“I think he knew the Russians were looking for an opportunity or a pretext to seize South Ossetia and Abkhazia. He felt he had a last opportunity to consolidate South Ossetia because the Russian plan was already laid.”

Critics say Mr. Saakashvili grew into a populist demagogue with a ruthless lust for power after he returned to Georgia in October 2000 as justice minister, under the then-president, Eduard Shevardnadze, who had met him in New York.

He ousted his former mentor in the bloodless Rose Revolution of 2003 and was greeted by the West as a hero who would spread democracy and freedom in the region. After becoming Europe’s youngest president, he moved his country toward membership of NATO, led a successful crusade against corruption, and saw Georgia praised globally as a beacon of democracy.

But now his critics will say his impetuousness triggered a crisis of Cold War proportions.