No need to try harder, it's not issue of PHD. 
"O you who have believed, obey Allah and  obey the Messenger and ALL SO OBEY  those in  authority among  you"
What's difficult to understand here apart from someone being third in line in authority. And Muhammad s.a.w introduced them. Why do I need to try harder? You're the one who needs to save Saqifa and to protect those who kicked it off.
Hmm... let us see once again:يَا أَيُّهَا الَّذِينَ آمَنُوا 
أَطِيعُوا اللَّهَ وَأَطِيعُوا الرَّسُولَ وَأُولِي الْأَمْرِ مِنْكُمْ  ۖ فَإِنْ تَنَازَعْتُمْ فِي شَيْءٍ فَرُدُّوهُ إِلَى اللَّهِ وَالرَّسُولِ إِنْ كُنْتُمْ
 تُؤْمِنُونَ بِاللَّهِ وَالْيَوْمِ الْآخِرِ ۚ ذَٰلِكَ خَيْرٌ وَأَحْسَنُ تَأْوِيلًا
(Sahih International)
O  you  who  have  believed,
  obey Allah and  obey  the  Messenger  and  those  in  authority among  you .  And  if  you  disagree  over  anything,  refer  it  to Allah and  the  Messenger,  if you  should  
believe  in Allah and  the  Last  Day.  That  is  the  best  [way]  and  best  in  result.
-Sura An-Nisa', Ayah 59
Hmm... those in red above STILL doesn't sound like the obligation to believe in imamah at all. 
Obligation to "believe in something" should sound like those in blue:لَيْسَ الْبِرَّ أَنْ تُوَلُّوا وُجُوهَكُمْ قِبَلَ الْمَشْرِقِ وَالْمَغْرِبِ وَلَٰكِنَّ الْبِرَّ مَنْ 
آمَنَ بِاللَّهِ وَالْيَوْمِ الْآخِرِ 
وَالْمَلَائِكَةِ وَالْكِتَابِ وَالنَّبِيِّينَ  (Sahih International)
Righteousness is not that you turn your faces toward the east or the west, but [true] righteousness is [in] one who 
believes in Allah , the Last Day, the angels, the Book, and the prophets.-Sura Al-Baqarah, Ayah 177
آمَنَ الرَّسُولُ بِمَا أُنْزِلَ إِلَيْهِ مِنْ رَبِّهِ وَالْمُؤْمِنُونَ ۚ كُلٌّ 
آمَنَ بِاللَّهِ وَمَلَائِكَتِهِ وَكُتُبِهِ وَرُسُلِهِ   لَا نُفَرِّقُ بَيْنَ أَحَدٍ مِنْ رُسُلِهِ ۚ وَقَالُوا سَمِعْنَا وَأَطَعْنَا ۖ غُفْرَانَكَ رَبَّنَا وَإِلَيْكَ الْمَصِيرُ
(Sahih International)
The Messenger has believed in what was revealed to him from his Lord, and [so have] the believers. All of them have 
believed in Allah and His angels and His books and His messengers,[saying], "We make no distinction between any of His messengers." And they say, "We hear and we obey. [We seek] Your forgiveness, our Lord, and to You is the [final] destination."
-Sura Al-Baqarah, Ayah 285
يَا أَيُّهَا الَّذِينَ آمَنُوا 
آمِنُوا بِاللَّهِ وَرَسُولِهِ وَالْكِتَابِ الَّذِي نَزَّلَ عَلَىٰ رَسُولِهِ وَالْكِتَابِ الَّذِي أَنْزَلَ مِنْ قَبْلُ ۚ وَمَنْ يَكْفُرْ بِاللَّهِ وَمَلَائِكَتِهِ وَكُتُبِهِ وَرُسُلِهِ وَالْيَوْمِ الْآخِرِ فَقَدْ ضَلَّ ضَلَالًا بَعِيدًا
(Sahih International)
O  you  who  have  believed,  
believe  in Allah and  His  Messenger  and  the  Book  that  He sent  down  upon  His  Messenger  and  the  Scripture  which  He  sent  down  before. And whoever  disbelieves  in Allah ,  His  angels,  His  books,  His  messengers,  and  the  Last  Day has  certainly  gone  far  astray.
-Sura An-Nisa', Ayah 136
A bit more harder, please, and without tahreef too!