BUDAPEST (Reuters) - Hungary's right-wing nationalist Prime Minister Viktor Orban seeks a third consecutive term in parliamentary elections on Sunday after scoring two landslide victories in 2010 and 2014.
Most opinion polls show that the best Orban's Fidesz party can achieve is winning a simple majority, which is also the likeliest outcome as Fidesz has a firm lead in opinion polls.
But there is an odd chance that the fractured opposition could push Fidesz into a minority and create an unprecedented hung parliament.
Orban is the European Union's second-longest-serving government leader after Germany's Angela Merkel.
He has led opposition in the bloc's eastern wing against a quota system, backed by Merkel and Brussels, to distribute migrants across the EU. He is also a leading opponent of efforts to deepen the bloc's integration.
His Fidesz party and its Christian Democrat ally KDNP won more than two thirds of parliament seats in the previous two elections.
Hungary's election graphics: https://tmsnrt.rs/2IS7mBl
HOW DOES THE ELECTION SYSTEM WORK?
Hungarian voters will elect 199 members into parliament in a single round. A total of 106 seats can be won in single-member constituencies in a first-past-the-post system. Party and ethnicity lists fill another 93 seats. Winning candidates have their surplus votes added to national party lists.
TURNOUT LEVELS AND OTHER FACTORS TO WATCH
* Some pollsters said voter turnout above 70 percent could signal efficient opposition mobilisation which may cause Fidesz to lose its parliamentary majority. The participation record, set in 2002, is 72 percent.
* High turnout may also push some smaller opposition parties below the five percent entry threshold. Green liberal Politics Can Be Different (LMP) and the social liberal Democratic Coalition hover around the threshold in polls.
* Opposition candidates need to win in 40-45 districts to deny Fidesz a majority, said Tibor Zavecz of pollster Zavecz Research.
* Janos Kovacs, chief analyst of pollster Iranytu, which is close to the largest opposition party Jobbik, put that critical threshold at 43-45 districts. "Much will also depend on (party) list votes," he added. "Estimating mandates is tougher than any time since 1990."
* According to opinion polls, Jobbik is likely to place second. Jobbik has ruled out coalitions with either Fidesz or establishment leftist parties.
HOW FIDESZ TWEAKED THE ELECTION LAW IN ITS FAVOUR
Election rules have been amended by Fidesz since 2010, boosting the ruling party's election chances against a fragmented leftist opposition and the rightwing Jobbik party.
* The total number of seats was reduced from 386 to 199 in 2011. The ratio of constituency seats rose to 60 percent from less than 50. District boundaries have been redrawn, and critics say gerrymandering was significant.
* A second voting round was eliminated, denying parties the option of clinching deals between the rounds, which contributed to the splintering of the current opposition.
* The system of voter compensation was changed in favour of winning candidates. In local districts, any vote not used to win a first-past-the-post race is added to national lists, including for the winner.
* The Fidesz government gave ethnic Hungarians the right to citizenship. They can vote on party lists, by letter. According to National Election Office data, 378,000 such new citizens have been registered for the 2018 election. A vast majority of them support Fidesz.
* Mail ballots were outlawed for hundreds of thousands of ordinary Hungarians working abroad, who are not necessarily Fidesz supporters. They can only vote in person at Hungarian embassies or consulates, limiting their ability to participate.
* The National Election Office mandated parties must field candidates in at least 27 local districts to maintain a national list and receive state support for their campaign, limiting options for parties to cooperate.
(Reporting by Sandor Peto, Editing by William Maclean)