One of the hardest jobs in politics is to defeat an incumbent member of the United States House of Representatives. In the last five elections, the percentage of incumbents who have been reelected was 98, 98, 96, 98 and 94.

Missouri has nine House seats. Eight incumbents — four Democrats and four Republicans — are seeking reelection this fall. All of them have safe seats. The only change will occur in the 9th Congressional District; the incumbent, Kenny Hulshof, is giving up his seat to seek the Republican nomination for governor. Eight candidates — four Republicans and four Democrats — are running in the Aug. 5 primary to succeed him.

Republicans: Irrespective of their political beliefs, none of the four GOP candidates has demonstrated the seriousness of purpose or the grasp of issues necessary to represent adequately the district’s approximately 620,000 residents.

The candidates differ little on the issues. None of them displays any command of policy. Their campaigns are based on platitudes and, in some cases, misinformation. We can’t recommend any of them.

• State Rep. Bob Onder, 46, of Lake St. Louis, a physician, is running as the “family values” candidate. Dr. Onder, with the help of Missouri House Speaker Rod Jetton, played a prominent role in the last legislative session, sponsoring bills to crack down on undocumented immigrants and on abortion providers. Mr. Jetton also works as a political consultant for Dr. Onder. Whatever their party, voters concerned about ethics in government should find Mr. Jetton’s double duty troubling, as well as Dr. Onder’s role in it.

• Blaine Luetkemeyer, 56, a former state representative and former Missouri Director of Tourism from St. Elizabeth, is promising voters to stop a “massive job-killing $1.2 trillion a year income tax hike that the liberal Congress has planned.” We have never heard of this plan, and Mr. Luetkemeyer could not provide details. He may be confusing it with the Lieberman-Warner “Climate Security Act,” although he said that was not the case. Candidates shouldn’t make stuff up.

• State Rep. Danie Moore, 62, of Fulton, is a retired school teacher who was a reliable GOP foot soldier in her eight years in the House but had no significant legislative accomplishments. Nor does she demonstrate much knowledge of current policy issues.

• Finally, there is Brock Olivo, 32, of Columbia, a business consultant and a former University of Missouri football star. His campaign got off to a rough start when he admitted that he had never voted in an election, but he is a very likeable young man. He doesn’t know much about the issues, but at least he admits it.

Democrats in the 9th District have just the opposite problem. All four of the candidates in the party’s primary have at least some grasp of policy.

• Steve Gaw is our choice. His credentials are impeccable: He is a former speaker of the Missouri House who knows how to build coalitions and move legislation. He spent four years on the Missouri Public Service Commission, two of them as chairman, and is intimately familiar with how energy and regulatory issues affect consumers. He has a law degree and a degree in physics and — important in this largely rural district — raises saddle horses and farms in Holts Summit. We disagree with his support for increased offshore oil drilling, but we respect the intellectual rigor he brings to his positions.

• State Rep. Judy Baker, 48, of Columbia, spent four years the Missouri House and was a generally reliable progressive vote during years of Republican control, but she cannot match Mr. Gaw’s leadership experience. A medical administrator, she would bring an expert’s perspective to congressional debates about health care. She is a coalition builder in her own right: She is a pro-choice candidate who has been endorsed by the women’s political advocacy group Emily’s List, and she also serves as a deacon at Columbia’s First Baptist Church, where her husband is pastor.

• Ken Jacob, 59, a lawyer and former longtime state legislator, is the most liberal candidate in the race. He has a long record of aggressive advocacy for progressive causes. But in an interview, he was unfamiliar with the agricultural issues that are crucial to the people of the 9th District.

• The wild card in this race is Lyndon Bode, 44, of Palmyra, an old-school “courthouse Democrat” in a part of the state often called “Little Dixie.” The presiding commissioner of Marion County for the last 14 years, Mr. Bode is conservative on most social issues but an aggressive advocate of public works spending. In Congress, he said, he would vote with the conservative “Blue Dog” Democratic coalition on many issues.