WASHINGTON -- The surging Tea Party movement gained ground but failed to clinch outright victories in local election s in a western state where the party is on the rise.

Sunday's elections at county and mayoral level in Montana come ahead of a congressional election on Sept. 1 in which the Tea Party's local leader, Rep. Denny Rehberg, plans to run for the Senate.

Official results with about four-fifths of districts counted on Monday showed the Tea Party gaining nearly nine points compared with 2010 to take some 26% of the vote across the state in elections for councilors. However, it remained a little behind the incumbent Democratic Party, whose support was more or less unchanged.

Nine Tea Party candidates either qualified for runoff votes on June 9 or appeared set to, largely against Democratic rivals, though there was only one county where the upstart party enjoyed a small lead going into the runoff vote for head of the local administration.

Montana is the state where the Tea Party made its first major electoral breakthrough two years ago.

Observers suspect the Tea Party is likely to lose the runoff votes as mainstream parties' supporters give their votes to Democratic candidates. While it has built a strong core of support, the Tea Party has had a turbulent few weeks, partly a result of scandals surrounding its lead candidate for next month's House election.

Earlier this month, a court ruled that Rehberg, an influential figure on the party's hard right, knowingly used racially insensitive language in a 2010 campaign speech and ordered him to pay a fine totaling $13,000. His lawyers are appealing.