Newcastle United is no longer as tough as last season against big teams, especially this season. I don't think Newcastle will threaten Liverpool much at the moment, unless Liverpool feel Newcastle is their biggest threat in maintaining their position at the top of the standings. Liverpool must be able to maintain its good performance if they don't want to lose their position at the top of the standings, otherwise Manchester City will be very ready to take over the standings and lead it.
Newcastle United don't have excellent and stable form like the past season but it is wrong to consider they are too much weaker than the past season. If Liverpool underestimate Newcastle United, they will have to pay very expensive cost. Newcastle United have enough good players to punish any defensive mistakes from Liverpool.
Newcastle United performed well at the start of the Premier League season, winning against big clubs and scoring plenty of goals against their opponent. Since Newcastle United started playing in the uefa champions league, Newcastle United's performance has reduced and they find it hard to win their matches.