NEW YORK - US President Barack Obama has a 5-point national lead over Republican challenger Mitt Romney in a new NBC News/Wall Street Journal poll released Wednesday. The president has been trending up after a successful Democratic convention and his response to the attacks on American embassies in the Middle East. He leads Romney 50 percent to 45 percent among likely voters. Optimism on the economy, according to the pollsters, is the driving force behind Obama’s strong polling. The number of Americans who think the country is on the right track improved by 7 points, to 39 percent.“Forty-two percent of voters also believe the economy will improve in the next 12 months, which is a 6-point jump from August, and a 15-point rise from July,” according to NBC’s FirstRead blog. “What’s more, 47 percent of registered voters approve of the president’s handling of the economy - up 3 points from last month. Obama’s overall job-approval rating stands at 50 percent for the first time since March.”