First Syria showed that even when a US President issues a "red-line", nothing much happens even if you cross it with chemical weapons. Then Russia discovered that you could really put the needs of a Russian minority in a sovereign nation (Ukraine) over the protests of a US President. Then Iran weathered two different US Secretaries of State (Clinton and Kerry) to maintain their goal of developing a nuclear weapons program and now have no problem rejecting international inspection of the nuclear facilities or permitting access to Iranian nuclear scientists. Oh and let's not forget Iran had no qualms about sending their warships up against ours in Yemen. Now China has issued warnings (at least 8 according to CNN) to US surveillance aircraft to "Go away" from international waters around the new contested artificial islands. Over these signs, no more like billboards, that our potential adversaries no longer fear US actions we have Mr. Obama assuring us that the loss of Ramadi is only a "setback" and assures us that we aren't losing to ISIS.
Mr. Obama and Mr. Kerry (with able assists from Valerie Jarret and Mrs. Clinton) have largely contributed to why the US is no longer seen as a superpower but they are not completely to blame. The actions leading to the downfall of the US actually has roots in one of the greatest victories of the former superpower. William Astore wrote a piece titled, "A Military Without Limits" in which he offers a compelling argument that a US military that no longer has the Soviet Union to keep in check has become ineffective. The Soviet military offered a check & balance to the US military industrial complex. Just as the Soviet Union could not just go wherever it wasn't already, the US military could only go so far without incurring retaliation from the Soviets.
Then two things happened almost simultaneously. The US handily stomped Iraq into the ground in less that 100 hours during Desert Storm (after a six month build-up it should be noted). Later in that same year the Soviet Union fell. The US had won two wars in a single year but with it came the realization that no one was left that could challenge the US. Desert Storm had proven that precision bombing had finally become a reality and softened the Iraqi forces up to where US ground troops literally ran over the top of them. The US military could truly now claim "anywhere, anytime".
With no real opponent in sight, and with the same Cold War structure and inventory of nuclear weapons, the US military would need to eventually find another opponent. It find it in Al Qaeda and actually went back on itself to fight another counter-insurgency war (which the post-Vietnam military had vowed wouldn't happen again).
We now have a military that has been exhausting its personnel and equipment for 13 years against in an "asymmetric"war yet at the same time, senior military officers want to buy the next generation weapon systems (F-35 for example). The US military had drawn down much of its overseas presence in Europe and the Pacific at the end of the Cold War but it ramped up the staging of news bases throughout the Middle East and former Soviet Republics.
But the problem in waging counter-insurgency wars is that often fighting one group (Al Qaeda) tends to lead to the creation of other groups (ISIS) before the first group is destroyed. Unlike fighting established militaries, insurgency groups can disappear and reform at the blink of an eye leaving formal military organizations such as the US with nothing to show for the efforts.
Presidents George H. Bush, Clinton, George W. Bush and Obama have all played an part in using what is still largely a Cold War structured US military to fight insurgents. Not only have the insurgents remained around but now other formal militaries are getting the bright idea that they just might win if they pick a fight with the US. Strange times indeed.