Recent opinion polls say Seguro will collect twice as many votes as Ventura in the head-to-head between the two top candidates in last month's first round of voting, when none of the runners captured more than 50 per cent of the vote required for victory.

But making it through to the runoff is already a milestone for Ventura and his Chega (Enough) party, which has quickly grown into a significant force in Portuguese politics during a wider European shift to the right.

Seguro, a longstanding Socialist politician, has positioned himself as a moderate candidate who will cooperate with Portugal's centre-right minority government, repudiating Ventura's anti-establishment and anti-immigrant tirades.

In Portugal, the president is largely a figurehead with no executive power. Traditionally, the head of state stands above the political fray, mediating disputes and defusing tensions.

However, the president is an influential voice and possesses some powerful tools, being able to veto legislation from parliament, although the veto can be overturned. The head of state also possesses what in Portuguese political jargon is called an “atomic bomb,” the power to dissolve parliament and call early elections.

In May, Portugal held its third general election in three years in the country's worst bout of political instability for decades, and steadying the ship is a key challenge for the next president.

Ventura, an eloquent and theatrical politician, has rejected political accommodation in favour of a more combative stance. One of his main targets has been what he calls excessive immigration, as foreign workers have become more conspicuous in Portugal in recent years.

“Portugal is ours,” he said.