Since the day he was elected, Obama has treated Congress like a lazy set of his own personal scribes. If they wrote whatever law he wanted them to, he patted them on their heads and told them, "Good job." If not, he just sighed and wrote whatever he wanted into law anyway, then chastised them publicly for being terrible at passing laws exactly the way he wanted them passed.
Immediately after he was elected, Republicans in the House met with Obama and expressed some concerns about the the early items on his agenda, including the size and allocation of the stimulus funds. As soon as they started talking, Obama interrupted Boehner and said, "I won," and then terminated the meeting, thus setting the tone for the entirety of his Presidency.
When Obamacare could not actually garner the support it needed to pass under regular order due to the fact that Scott Brown was elected specifically to stop it from passing, Democrats (with the full blessing of Obama) passed it under reconciliation even though it was not a budget bill.
When Democrats became skittish about the electoral consequences of the deadlines and penalties associated with Obamacare, Obama repeatedly just essentially rewrote the law without Congress by extending statutory deadlines, treating them as optional, or just not enforcing them at all. At no point did he ever even contemplate approaching Congress and asking them to change these deadlines in accordance with their prerogative to change or modify existing legislation.
When Obama started stacking independent agencies with radical leftists who could not gain Senate support via abuse of the recess appointment clause, the House exercised their constitutional prerogative not to recess, thus preventing the Senate from recessing (again under the express text of the Constitution. Obama decided that the sole power to determine whether the Congress was actually in recess belonged to him and him alone, and made a bunch of recess appointments even though Congress was definitely not in recess. This blatantly unconstitutional action by Obama had absolutely no chance of succeeding, and wasted billions of federal dollars before every action taken by the agencies he packed was nullified by a unanimous Supreme Court.
Not content with thumbing his nose at Congress's constitutional authority to set the terms and duration of their own recess, Obama directly violated Congressional statutes on countless occasions, including clearly expressed federal law which required him to notify Congress before attempting a prisoner swap like the one in which he sent multiple dangerous terrorists back to Afghanistan in exchange for deserter Bowe Bergdahl. The Obama administration actually admitted that they broke the law with respect to Bergdahl, but basically excused this by saying "It was super important, guys."
After the American people told Obama where he could stick his legislative agenda by sending humongous Republican majorities to both houses of Congress in 2014, Obama openly declared that he DGAF what Congress thought about anything, because he had a "pen and a phone." Sure enough, immediately afterwards, Obama started using his "pen and phone" to stomp all over Congressional prerogatives. He entered into a treaty with Iran even though he clearly did not have Senate approval for a treaty.
After Congress mustered the will to pass the Corker-Cardin deal (which Obama signed!) the Obama administration blatantly violated Corker-Cardin (and other pre-existing Federal law) by releasing sanctioned funds without Congressional approval or without even meeting the terms of their own agreement.
When Congress did not pass the Immigration reform bill that Obama desired, Obama simply wrote one into an executive order and started carrying it out before he was enjoined from continuing to do so by multiple Federal courts.
When Congress did not pass a cap and trade bill that Obama desired, Obama simply wrote one into an executive order and implemented it until the Supreme Court struck it down just a week ago.
On multiple occasions, Obama has likewise attempted to implement executive orders on gun control expressly because the Congress refuses to acquiesce to his abridgement of Americans' Second Amendment rights.
So now here comes Obama, declaring that he is going to nominate a replacement for Scalia, the greatest conservative Justice who ever lived, and it is his constitutional right to do so. Let him nominate as many people as he wants. There's nothing in the constitution that says the Senate has to say "yes," a concept that many Democrats seem inexplicably unclear on.
Here, at least, is a chance for McConnell et al to prove to people that a Senate majority means something. All this time, McConnell and his cronies have decried using the power of the purse to shut down the Federal government or to curtail Obama in any way, shape, or form. If Republicans balk at Obama's appointment - no matter who it is - they will not shut down the government or stop an essential governmental function. The Supreme Court has gone for an entire term with only 8 justices due to health reasons before, and even if the Republican Senate was working aggressively to confirm Obama's nominee, they could likely not get it done before the end of the summer term anyway.