WASHINGTON —  When Joe Biden tells voters he understands the threat posed by Afghan extremists, he dramatically illustrates one reason why: His helicopter was "forced down" on "the superhighway of terror." Actually, snow, not the enemy, persuaded the helicopter pilot to land and wait out a storm.

The Democratic vice presidential candidate has repeatedly left that part out, in an episode that Republicans hope will become an echo of Hillary Rodham Clinton's errant tale during the primaries of landing in Bosnia under sniper fire.

Biden has made a number of questionable statements recently that, viewed in isolation, might not amount to much. But this is a man whose first presidential campaign collapsed 20 years ago after he told a story about coal miners in his family that he lifted without credit from a British politician.