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It's hard to really say much or little. At the beginning of the season everyone wrote Leverkusen off, but now they are four points behind Bayern. Only half of the season has passed and if Liverkusen remain stable, then we can start to think that it is dangerous for Bayern, but now I agree with you that they are very far from the first place, Bayer play a lot of draws.
The pressure from Leverkusen makes the competition more challenging, Xabi Alonso just needs to maintain his team's performance so as not to slip under any circumstances to keep the competition alive. Anything can happen in the second half of the season, including Bayern Munich dropping points like they did against Mainz. The four-point gap is not too far, there is still a possibility of a change in position if Bayern Munich is unable to maintain the consistency they have shown so far.
Dortmund are looking to get back into the top four, they could spring a surprise in the second half of the season having been a regular team to qualify for the Champions League. They are also a threat to other big teams because they always appear different when competing in Big Match games.