Sen. Rand Paul (R-Ky.) is getting widely panned for apparently flip-flopping on aid to Israel. He denies he has, but a whole lot of people across the political spectrum don’t buy his explanation. He also denied changing his mind on the Civil Right Act. That brings us to a perennial presidential election issue: When is it acceptable to change your mind and when does flip-flopping spell political doom? That latter hurt Sen. John Kerry (D-Mass.) in 2004 and Mitt Romney in 2008. Still, other pols have changed or modified their views and come out just fine.

Sen. Rand Paul, R-Ky. speaks at Faith and Freedom Coalition's Road to Majority event in Washington, Friday, June 20, 2014. Organizers said more than 1,000 evangelical leaders were attending the conference, designed to mobilize religious conservative voters ahead of the upcoming midterm elections and the 2016 presidential contest. While polls suggest that social conservatives are losing their fight against gay marriage, Republican officials across the political spectrum concede that evangelical Christian voters continue to play a critical role in Republican politics. (AP Photo/Molly Riley) Sen. Rand Paul (R-Ky.) (Molly Riley/Associated Press)

Here are some clues as to whether an about-face is going to be a problem: Is it part of a pattern of convenient modifications? Is it recent, such as Hillary Clinton on gay marriage? Did the pol explain the change in a convincing fashion or simply deny the change? Is the change of heart clear and captured on video (therefore easily used in ads as was Kerry’s remarks that “I actually did vote  for the $87 billion before I voted against it“)? Do the candidate’s aides have to continually “clarify” or walk back statements that sound strange (e.g. Rand Paul’s remarks on World War II, Dick Cheney and Vladimir Putin)?

Despite the fear of being labeled a flip–flopper, circumstances do change and pols who refuse to consider new information or circumstances can look stubborn or out of touch. Hillary Clinton clinging to the notion that Russian reset worked out well falls into this category.

There are examples of smart and reasonable shifts on major issues that the public can stomach. On the gay marriage issue, pols — as we have seen in several instances, including Wisconsin Gov. Scott Walker — have essentially said they still believe in “traditional” marriage but the plethora of court cases and popular referenda have made the issue moot. Likewise, I don’t find anything wrong with Sen. Marco Rubio (R-Fla.) saying he certainly championed comprehensive immigration reform but, as political matter, understands that a border-security-first measure will have to be adopted.

There is also a matter of priorities. Many Republicans voted for the Budget Control Act of 2011 but now favor putting money back into national security. It is reasonable to explain that this was the only deal at the time that would have kept the country out of default, but that world events have emphasized the need to rebuild our armed forces. Some Republicans voted against the BCA because of defense cuts and will be able to boast about their far-sightedness. That said, there is a difference between flip-flopping for convenience and being guilty of lack of foresight, although the latter is still a problem. In this category we would put the vote on authorization against use of force against Bashar al-Assad for using weapons of mass destruction. Some lawmakers didn’t see how that might play into Iran’s calculus. Wising up now, in that case, is at least a sign the pol can learn and fess up to mistakes.

People do change their minds in real life. And many voters think all pols are slippery so don’t put a lot of stock in about-faces. Nevertheless, it becomes a matter of character when you do it frequently and then deny you have.