JACKSON, Mississippi (AP) — Six-term U.S. Sen. Thad Cochran campaigned with leading figures of Mississippi's Republican establishment and cast himself as a reliable opponent of President Barack Obama on Monday — the eve of a primary showdown with a conservative rival.

The race drew much of the attention among primaries across eight states on Tuesday. Nominations for the Senate are on the ballot in Alabama; Iowa; Montana; New Jersey; New Mexico and South Dakota as well as Mississippi in a year in which Republicans need to gain six seats to win a majority. Gubernatorial primaries are taking place in Alabama, Iowa, New Mexico, South Dakota and California, where Democratic Gov. Jerry Brown is seeking a fourth term this fall.

Cochran's rival, Chris McDaniel, made the final rounds of his campaign and carried with him the hopes of conservative, anti-tax tea party supporters nationwide eager to topple a high-profile Republican incumbent in this year's primaries. In an interview between stops, he said he wants to "end cronyism in Washington, D.C," and "repeal Obamacare in its entirety" He said he'll also push for term limits and a constitutional balanced budget amendment.

Democrats face a distinctly uphill battle to win a House majority this fall, and they and their allies sought to knock out Republican contenders in primaries in California and New Jersey.

The House Majority political action committee aired a television ad against Republican hopeful Doug Ose in California in an apparent attempt to help a more-conservative Igor Birman win a spot on the ballot. Seizing on votes cast in 2003, when he was in Congress, the ad said, "Doug Ose didn't serve the troops — he just served himself."

Ose has criticized the ad, but its mere existence was evidence that party officials believe Birman would present a weaker challenge to Democratic Rep. Ami Bera in the fall.

A 50 percent threshold is necessary to avoid a runoff in Mississippi's tough Senate Republican challenge, hardly a certainty in a race with a third candidate.

Cochran, 76, who has brought billions of federal dollars to his state, campaigned with Gov. Phil Bryant and Rep. Gregg Harper as he worked to fend off McDaniel's challenge.

Neither he nor Harper nor the governor mentioned McDaniel by name, but the references were hard to miss.

"Thad Cochran will never do anything to embarrass the state of Mississippi," Harper said in an appearance at the Mississippi Agriculture and Forestry Museum in Jackson.

An independent group that supports Cochran, Mississippi Conservatives, mailed a card to thousands of voters recently saying McDaniel would embarrass the state. The card played a few seconds of a talk radio audio recording of McDaniel from a decade ago, in which he said he had heard the word "mamacita" was a good pickup line for Mexican women.

But the main controversy of the race was the arrest of four men on charges they surreptitiously photographed Cochran's wife in a nursing home where she has lived for more than a decade with dementia.

Cochran's campaign seized on the arrests, airing a television commercial that said the four are McDaniel's backers, and saying, "Rise up and say, 'no' to dirty politics."

McDaniel has said his campaign knew nothing of the incident until after it occurred.

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Associated Press writer Tom Beaumont in Iowa contributed to this report.