AP

WASHINGTON A CHALLENGE to a Republican stalwart in the Senate in Tuesday’s Indiana primary election could, once again, backfire and play into the hands of Democrats who are struggling to retain control of the upper chamber in Congress.

The insurgent tea party wants to eject moderate Republican Senator Richard Lugar in favour of a hardline conservative. Lugar and Utah Senator Orin Hatch, who also faces a tea party opponent in that state’s primary in late June, are the two longest serving Republicans in the Senate. The tea party movement, which advocates small government, deep spending cuts and no tax increases, has labelled both senators as Washington insiders and castigates them for compromising with Democrats over their long careers.

Polls in Indiana show, however, that tea party backing for state Treasurer Richard Mourdock, a deeply conservative Republican, could produce a replay of Senate elections in 2010.

Then, tea party-backed Senate candidates ousted the party establishment’s choice in several state primaries.

But the more extreme candidates cost the Republicans possible Senate pickups in the general election in Colorado, Delaware and Nevada, leaving the Senate narrowly in Democrats’ hands In Indiana, polls show Lugar handily defeating Democratic candidate US Representative Joe Donnelly in the November vote, but when voters were surveyed about Mourdock’s chances against Donnelly, the men were running neck and neck.

Regardless, Mourdock is opening a lead over Lugar, who is seeking a seventh sixyear- term in the Senate.

The danger facing Lugar is a direct result of the US system of choosing party candidates in state primary elections.

Those votes typically are dominated by the most conservative Republicans and the most liberal Democrats, voters motivated to turnout for a primary election. The system also skews the candidate choice away from the more centrist inclinations of the totality of a state’s electorate when the November election rolls around.

That’s what happened in 2010 when the tea party forced extreme conservative Senate candidates onto the ballot only to see them defeated in the general election.

In that vote Democrats in those match-ups would have been vulnerable to a more moderate Republican challenger.

Lugar has moved to the right and like Utah’s Hatch is trying to shore up his right flank by more vociferously opposing Obama’s policy initiatives.

Hatch is taking a lesson from the experience of fellow Utah Senator Bob Bennett. He was defeated by a tea party-backed challenger at the 2010 Utah Republican nominating convention.

Hatch won nearly 60 percent of the vote at this year’s Utah Republican convention, but just fell short of avoiding a June 26 primary against former state Senator Dan Liljenquist who enjoys tea party support. No Democrat has been elected to the Senate from heavily Mormon Utah since 1970.