Most people accept the notion that politicians don’t always tell the truth. Some lies are harmless enough; others more consequential.

Lyndon Johnson skirted the truth when he promised during the 1964 presidential campaign not to send any more American troops to fight a land war in Southeast Asia. He knew then that American intervention would eventually be necessary, but the lie helped him win the election. After the election, Johnson sent additional troops, more American lives were lost and the war escalated.

Richard Nixon claimed he knew nothing about Watergate. “I am not a crook,” he said. Lies.

In 1976, Jimmy Carter promised never to lie to us, a promise that rested on a perception of his own virtue. Given his sad record, the country might have willingly exchanged veracity for competence.

Bill Clinton? We know about one of his most famous lies, emphasized by that wagging finger and video showing him lying under oath as he labored to define the word “is.” Clinton’s lies led to his impeachment. The public didn’t seem to care that much because as Democrats and the media repeatedly said, it was “just about sex” and everyone lies about sex.

Former CBS News anchor Dan Rather had a curious spin on lying when he told Fox’s Bill O’Reilly that even though Clinton lied about not having sex with Monica Lewinsky, he still believed Clinton to be an honest man: “I think you can be an honest person and lie about any number of things,” said Rather.

George W. Bush was accused of lying when he justified invading Iraq and toppling Saddam Hussein by claiming he had weapons of mass destruction. WMDs were never found.

President Obama’s most famous lie (so far) has been his promise: “If you like your (insurance) plan you can keep it.” Same with your doctor, he said. And he promised health insurance and treatment costs would go down under Obamacare. Not for everyone. Oops.

According to CNN.com, former congressional chief of staff and Washington lobbyist Ed Uravic, author of the book “Lying Cheating Scum,” claims, “Every president has not only lied at some time, but needs to lie to be effective.”

A president can lie up to a point, but when a president’s lies extend beyond protecting the country (white lies) and drift into a darker area that is self-serving (black lies) it is something quite different, often prompting public rejection when he’s exposed.

Speaker John Boehner says he and his fellow Republicans can no longer trust the president due to what they believe is his repeated lies. Last week, Boehner said House Republicans are not prepared to move ahead on immigration reform this year because they do not trust President Obama to follow the law. Boehner and his GOP colleagues are particularly disturbed by the president’s assertions he can go around Congress when he wants to, changing the health care law and writing executive orders when it suits his fancy.

Claiming an American president is not trustworthy ruins whatever credibility he brought to the office and this president brought a lot. Most people wanted to believe in him and a large majority did believe in him at the start. Many no longer do, as his declining approval ratings demonstrate.

In dealing with the Soviet Union, Ronald Reagan employed a Russian proverb, “trust but verify.” Boehner and the Republicans seem to be saying there is no need to verify with this president, because he can’t be trusted.

The inability by a major party to trust a president is more than lamentable; it is not good for the country and our standing before other nations and groups that wish to do us harm.

Cal Thomas is a syndicated columnist and author. Readers may email him at: tcaeditors@tribune.com.