The death toll from jihadist terrorism on American soil since the Sept. 11 attacks — 45 people — is about the same as the 48 killed in terrorist attacks motivated by white supremacist and other right-wing extremist ideologies, according to New America, a research organization in Washington. And both tolls are tiny compared with the tally of conventional murders, more than 200,000 over the same period. But the disproportionate focus they draw in the news media and their effect on public fear demand the attention of any administration.