Russian President Vladimir Putin's re-election on Sunday to a fourth six-year term comes amid a feeling both in the West and in Moscow that he is ascendant as a global leader and that Russia has reemerged as a global superpower. However, if one scratches beneath the surface of these assertions, it's clear that Putin faces a growing number of complex challenges that are likely to deepen in the coming months and gradually erode his political momentum. Here are a few that will be the most difficult for him to overcome.

In Syria, Russia is increasingly stuck on both the military and diplomatic fronts. On the battlefield, Putin has repeatedly boasted that Russia's military goals in Syria have been accomplished — the defeat of extremist groups threatening the regime of Bashar Assad — and that he soon plans to draw down Russian military forces. However, given the chaotic situation on the ground — the Assad regime still controls only about one-third of the country — that seems unlikely anytime soon.

The cost of Moscow's presence in Syria, meanwhile, continues to grow. In the past few weeks, the Russians have suffered the crash of a military transport with several senior officers on board, the downing of a Russian fighter jet by anti-government forces, a clash involving American-backed forces and Russian mercenaries that produced dozens of Russian casualties, and an attack by insurgents using drones on two of its bases. The latter reportedly damaged several Russian aircraft, and is likely to be repeated in the coming months.