By Johan Ahlander and Gederts Gelzis
RIGA (Reuters) - Latvians are set to vote on Saturday in parliamentary elections in which the rise of an anti-establishment party will test Riga's long-standing role as one of West's bulwarks against Russia.
Latvia, a member of the European Union and NATO, shares a 270-kilometer (167 miles) border with Russia which makes it a frontline state in the increasingly hostile relationship between the West and President Vladimir Putin.
NATO currently has more than 1,000 troops deployed in the Baltic country of 2 million and even the potential of a minor shift in allegiance in Latvia will worry both Brussels and Washington.
Latvia's mainstream parties have resolutely kept pro-Russian politicians from power as they sought ever closer ties with the West. At the last election, Harmony, a party whose main support is from Latvia's ethnic Russian minority, won the most seats but was excluded from power when the other parties refused to include it in any deal due to its ties with Russia.
But the populist KPV LV party and its leader Artuss Kaimins, whose popularity has soared as he railed against corrupt politicians, has sent mixed messages on whether he would also rule out such a deal.
"We are at a crossroads. Either we will form a new government or they will," said Prime Minister Maris Kucinskis of the Union of Greens and Farmers party.
A KPV-Harmony ruling alliance would represent "a rather radical change of Latvia's position toward the European Union and toward our security matters which, I think, is very dangerous," he said.
Kucinskis' conservative government coalition looks well short of winning a majority. Recent polls suggest Harmony will remain the biggest party, followed by the Union of Greens and Farmers and Kaimins' KPV LV.
Harmony, which currently holds 24 out of the 100 seats in parliament, recently rebranded itself as a Western-style Social Democratic party, saying it is committed to the European Union and NATO.
But it only ended its official cooperation agreement with Putin's United Russia Party last year, raising concerns its transformation is only skin deep.
Harmony could be used by Russia to influence EU affairs, said Andis Kudors, executive director of the Centre for East European Policy Studies.
"It (Harmony) is like a kind of Trojan horse in (the) European Union when we speak about common European Union foreign policy in regards to Russia."
The KPV backs EU and NATO membership, but its vague election program has left many wondering what could happen if it takes power.
Kaimins, who declined several requests from Reuters for interviews, has said he is open to working with Harmony if it condemns Russia's role in the conflict in eastern Ukraine and drops demands for Russian-language education in Latvian schools.
Harmony has not ruled out working with any party and has said KPVs voters will have to be respected.