In addition to Bayern Munich and Leverkusen, we also cannot miss Frankfurt who is the mediator of the competition between the two teams. Frankfurt will likely appear more consistent considering their schedule is not included in the Champions League. So this season Frankfurt can focus on maximizing their chances in the Bundesliga. Occupying 2nd position with a small difference from Leverkusen requires Frankfurt to be able to create distance.
Frankfurt can indeed be an obstacle for Leverkusen in terms of competing for its position in the Bundesliga standings, but Frankfurt must be willing to make improvements in terms of consistency because Frankfurt has also experienced two defeats and three draws during the thirteen weeks in the Bundesliga this season. So at least Frankfurt must continue to be able to win matches so that their position is not taken by Leverkusen even though Frankfurt is finding it more difficult to catch up with Bayern Munich who are currently at the top of the Bundesliga standings.
I cannot really vouch for Frankfurt at the moment due to their inconsistent run so far, though it seems like they are the team that poses some threat to Frankfurt in the league right now and they haven't been their best this season compared to previous seasons when they were in good form, but maybe they might just put their house together and start getting the right result but I still do not see them as a potential threat to the leverkusen side, at least not at the moment.
Leverkusen could be an obstacle for frankfurt in terms of competing for a better position in the Bundesliga standings this season, although they are currently above leverkusen, but honestly it will be a very difficult job for them to maintain their position from leverkusen at this time, because to doing so they must immediately improve their consistency which so far is still unstable, they have lost two and drawn three of their 13 Bundesliga games this season, so although they seem to be a team that could pose a threat to Munich in the league, but I don't think they are ready to challenge for the title with Munich although if they has show their best form this season.