By Greg Giroux, CQ Staff

Tuesday will be a busy day for voters in Texas and Ohio — and not just for the Democrats who are going to cast ballots in a pair of momentous contests between Sens. Barack Obama of Illinois and Hillary Rodham Clinton of New York.

Millions of voters in those two states — which together comprise one-ninth of the U.S. population — also will be making choices in primary elections for Congress, though those contests have attracted far less attention than to the Clinton-Obama showdown.

Four Democrats are vying to oppose Republican Sen. John Cornyn . The party-preferred candidate is state Rep. Rick Noriega, who’s been trying to cultivate a statewide presence in a low-profile contest in which little-known candidates Gene Kelly, Ray McMurrey and Rhett R. Smith also want the Democratic nomination. A Public Policy Polling survey in late February had Noriega way ahead, but with a large number of undecided voters.

Cornyn, who is seeking a second term, is expected to easily defeat Larry Kilgore, who badly lost a 2006 primary challenge to Republican Gov. Rick Perry .

Opportunities for Republicans to make gains in Texas include the 22nd District, where 10 Republicans are seeking to oppose Democratic Rep. Nick Lampson in a Republican-leaning area in and around Houston that Republican Tom DeLay represented from 1985 until his resignation in June 2006. With so many Republicans running, it seems clear that no candidate will win a majority of votes needed for an outright victory — and that the nomination will be decided in an April 8 runoff election between the top two finishers.

The Republican field includes Pete Olson, Cornyn’s former chief of staff, and Shelley Sekula Gibbs, a former Houston city councilwoman who served the remaining two months of DeLay’s unexpired term (but lost to Lampson in the election for the full term). They’ve been on the receiving end of criticism in a field that includes state Rep. Robert Talton; Dean Hrbacek, the former mayor of Sugar Land; John Manlove, the former mayor of Pasadena; and Jim Squier, a former judge.

Republicans are also looking to reclaim the 23rd District, which takes in part of San Antonio and most of the state’s border with Texas. Francisco “Quico” Canseco, a businessman, and Lyle Larson, a commissioner in the county that includes San Antonio, are seeking the Republican nomination; the winner will oppose Democratic Rep. Ciro D. Rodriguez , who unseated Republican Rep. Henry Bonilla in 2006 after a federal court redrew the 23rd to absorb more Democratic-leaning Hispanics in San Antonio.

No Texas incumbent appears to be at serious risk of losing renomination on Tuesday. In the 14th District, which takes in the southeastern Texas cities of Victoria and Galveston, Rep. Ron Paul is expected to defeat Chris Peden, a member of the city council in Friendswood — even though Paul technically is still a candidate for the Republican presidential nomination, thanks to a longstanding Texas law that allows him to seek both offices simultaneously. The Democrats did not field a candidate in Texas’ 14th.

In Texas’ 4th District, which takes in northeastern Texas, 84-year-old Republican Rep. Ralph Hall faces four primary opponents: businessmen Gene Christensen and Kevin George; Joshua Kowert, a graduate student; and Kathy Seei, the former mayor of Frisco. The Democratic primary contestants are VaLinda Hathcox, a lawyer, and Glenn Melancon, a college professor; the winner will be a distinct long shot in a district that gave President Bush 70 percent of the vote in 2004.

The only other Texas incumbent who faces opposition in Tuesday’s primary is six-term Democrat Silvestre Reyes , who represents the El Paso-centered 16th District and is the chairman of the Select Intelligence Committee. Reyes should easily beat Jorge Artalejo, a political unknown. No Republican filed to run.

In the 10th District, which takes in suburbs of Houston and Austin, two-term Republican Rep. Mike McCaul is unopposed in the primary and heavily favored to win again in November. But the Democrats will choose between two credible candidates — Dan Grant, who has a background in international affairs, and Larry Joe Doherty, a lawyer who played a judge in the courtroom television show “Texas Justice.”

OHIO

Like his Texas colleague Paul, Ohio Democratic Rep. Dennis J. Kucinich pursued a long-shot presidential campaign as he sought re-election to Congress. Kucinich ended his White House bid in late January, acknowledging concerns from labor leaders that he needed to concentrate fully on winning re-election in the northeastern 10th District.

The toughest of Kucinich’s four primary challengers is Joe Cimperman, a Cleveland city councilman who has portrayed Kucinich as an absentee congressman more interested in quixotic bids for the White House than in the day-to-day duties of representing his constituents on the west side of Cleveland and its suburbs.

Kucinich has ramped up his fundraising in recent weeks and emphasized his stances against the Iraq War and international trade pacts. He’s portraying himself as a scrappy fighter against “corporate interests” Kucinich says want him defeated.

The other Democratic primary candidates are Barbara Anne Ferris, who lost decisively to Kucinich in a 2006 primary; Thomas O’Grady, the mayor of North Olmsted, a Cleveland suburb; and Rosemary Palmer, a journalist and educator whose son died in Iraq.

The other notable primary challenge to an incumbent is in Ohio’s 2nd, where Republican Rep. Jean Schmidt is seeking a second full term. Schmidt faces state Rep. Tom Brinkman on Tuesday and could face a November contest with Democrat Victoria Wulsin, a physician who nearly defeated Schmidt in 2006 and whose chief primary opponent is Steve Black, a lawyer and former Republican.

In several Ohio districts, Tuesday’s vote will set up long-anticipated November matchups in politically competitive districts where Republicans are the defending party.

The only real opportunity for Republicans to gain a U.S. House seat in Ohio is in the 18th District, where four Republicans are vying to oppose freshman Democratic Rep. Zack Space in a culturally conservative area of southern and eastern Ohio. The top three Republican candidates are Paul Phillips, a lawyer and Air Force veteran; Jeannette Moll, a lawyer; and Fred Dailey, a former director of the Ohio Department of Agriculture.

In the 1st District, seven-term Republican Rep. Steve Chabot and Democratic state Rep. Steve Driehaus are unopposed in the primaries in a politically competitive district in and around Cincinnati where Chabot was re-elected in 2006 with 52 percent of the vote.

In the 15th District, which takes in part of Columbus and its suburbs, Democrat Mary Jo Kilroy is unopposed in the primary and will face the winner of a Republican primary in which the party-preferred candidate is state Sen. Steve Stivers. Kilroy in 2006 nearly defeated Republican Rep. Deborah Pryce , who is retiring after eight terms.

In the 16th District, a constituency in and around Canton that is being left open by retiring 18-term Republican Rep. Ralph Regula , Democratic state Sen. John Boccieri is expected to win his party’s primary and face the winner of a Republican primary that includes state Sen. Kirk Schuring, who has a political base in Canton, and Matt Miller, a county commissioner from the lesser-populated western end of the district who ran against Regula in a 2006 primary.

A highly competitive race might surface in Ohio’s 14th, where Republican Rep. Steven C. LaTourette is seeking re-election in the northeastern corner of the state. The congressman initially will be a strong favorite against the winner of a three-candidate Democratic primary that includes Bill O’Neill, a former state appellate judge.

The Republicans also will be defending the 7th District, which includes Springfield, a small part of Columbus and other territory south of Ohio’s capital city. Nine-term Republican Rep. David L. Hobson is joining Pryce and Regula in making the current 110th Congress their last, though the Republicans are more strongly favored to retain the 7th than they are Pryce’s 15th or Regula’s 16th. Republican officials expect that state Sen. Steve Austria will prevail on Tuesday and also defeat the winner of a six-candidate Democratic primary.