When the year began, Senate Majority Leader Mitch McConnell's number one priority was to quickly move forward with a plan to repeal Obamacare—but in a way that delayed the repeal while the GOP settled on some sort of replacement plan.

That plan came with many potential pitfalls, and now it looks as if it may not work out after all—thanks in large part to opposition from Sen. Rand Paul (R-Kentucky).

McConnell's intention was to use the reconciliation process, which allows the Senate to pass certain types of bills that are directly relevant to the budget with a simple majority, to strip out certain key components of the law, including its individual mandate, taxes, and insurance subsidies. Those changes, however, would not go into effect for somewhere between two and four years. During that time, the hope was that Republicans in Congress would finally work out some sort of replacement plan.