Merkley's proposal revolves around a single principle: the Senate should always allow debate. So the filibuster should be banned entirely on motions to proceed and on amendments because both are things the promote debate and engagement. Filibusters would still be allowed on a bill's final vote, but it would take more than one senator to launch a filibuster (Merkley suggests a minimum of ten) and senators would have to actually hold the floor and talk. No longer would a single person be able to obstruct all business just by dropping a note to his party leader.

And in return? The minority party would have one of its major grievances addressed: the ability to offer amendments to legislation. Merkley proposes that unless a different agreement is reached prior to a bill coming to the floor, each side would be allowed to introduce five amendments of their own choosing. No longer could the majority leader "fill the amendment tree" or otherwise prohibit the minority party from trying to amend legislation. This fits with his broad principle that debate and engagement with legislation is a good thing. The minority party might choose to offer mischievous or blatantly political amendments, but that's their choice. They also have the choice of genuinely trying to improve legislation and getting a majority of their colleagues to pass it. [...]

[Merkley's proposal] doesn't eliminate the filibuster, it just eliminates filibuster abuse. And in return, the minority party gets an expanded ability to engage in a positive way with any legislation on the floor.

...Merkley understands the reality of the modern Republican Party: they don't use the filibuster occasionally to obstruct legislation they feel especially strongly about, they use it "on nearly a daily basis, paralyzing the Senate." What's more, the filibuster isn't just a way of requiring 60 votes to pass legislation. Rather, "the filibuster can be thought of as the power of a single senator to object to the regular order of Senate deliberations, thereby invoking a special order that requires a supermajority and a week delay for a vote."

This is a key point to understand. The modern filibuster requires only one person to invoke it, doesn't require that person to do anything other than announce his intent, and automatically eats up a week or more of time on the Senate calendar even on legislation that's widely popular. Last year, for example, it took the Senate five weeks to approve an extension of unemployment benefits that eventually passed 98-0.