Yes, the fact that Bernie Sanders is gaining momentum in Illinois can slow Hillary Clinton down. Every vote that Bernie Sanders accumulates is a vote that could have gone to Hillary Clinton. Therefore, it makes little sense to believe that increases in Bernie Sanders momentum does not slow Hillary Clinton down. They are opposing candidates.
The headline says it all. Bernie has recently made news for gaining traction in the important state of Illinois, leading some to wonder whether or not he can slow Hillary's sweep of the country. Unfortunately, it appears he cannot. Hillary already has many, many more delegates than Bernie does - at this point, it would take a miracle for Bernie to slow her down, and Illinois will not be that miracle.
Hillary Clinton won the Illinois primary, as well as four other states that night. Bernie Sanders isn't gaining any momentum, but is still earning votes sporadically. He doesn't have what it takes to get the nomination from Hillary. She has already secured over half the delegates she needs, while Bernie has only about half as many as Hillary.
Bernie is a long shot to get the nomination at this point. After the Super Tuesday results on March 15th, Hilary showed that she wasn't going to be slowed down by winning all five states. While Bernie is projected to do better in the upcoming states, I feel that Hilary's lead has gotten too large at this point for Bernie to slow her down enough to win the nomination.