Barack Obama accused rival Hillary Rodham Clinton of trying to “scare up votes” with a new ad as the former first lady struggled to halt his sprint to the White House ahead of key Democratic presidential nominating contests next week.

Obama’s criticism came on Friday after Clinton unveiled an ad to run in Texas that showed images of sleeping children and asked which candidate would be more qualified to answer a national security emergency call at 3 a.m. The ad was designed to appeal to women voters — a core bloc Clinton needs in order to salvage her faltering campaign in the March 4 races in Texas and Ohio.

“We’ve seen these ads before,” Democratic front-runner said while campaigning in Texas. “They’re the kind that play on peoples’ fears to scare up votes. Well, it won’t work this time. Because the question is not about picking up the phone. The question is: What kind of judgment will you make when you answer?”

Obama’s string of 11 victories since the February 5 “Super Tuesday” contests has raised questions about the viability of Clinton’s candidacy. Her campaign announced Thursday that it had its best fund-raising month ever, securing USD 35 million, but aides and supporters concede she must win the Tuesday contests to remain competitive. A Fox News poll released Friday showed Obama moving into a narrow lead of 48 per cent to Clinton’s 45 per cent in Texas, but that was within the margin of error.