The Senate is Broken
The U.S. Senate is broken--and the Senators themselves have broken it with their adoption of the modern filibuster. The filibuster has deep roots, but they do not extend to the Constitution, only to an infamous vice president.
An argument that opened the door to a Senate filibuster was made in 1805 by Vice President Aaron Burr (then recently indicted for killing Alexander Hamilton in a duel). Once the door was opened to it, the Senate filibuster grew over many decades of rules changes, to make the U.S. Senate the place where legislation goes to die. Burr argued to "clean up" the Senate rules by dropping something called "the previous question," a motion to stop debate, stop consideration of amendments, and bring a bill to a vote. Before 1805 the U.S. House and the U.S. Senate played by the same rule book, but the House kept its "previous question" motion. In the U.S. House today a simple majority can force a vote on the bill at hand. In the House the retained "previous question" rule effectively prevents one or a few legislators from "talking to death" a bill under consideration even though a simple majority of Representatives are ready to vote on it. Not so in the Senate, where Burr's argument prevailed, the "previous question" rule was voted out in 1806, and the filibuster became possible.
Historically, "talking to death" a piece of legislation is how the filibuster works. Without the "previous question" rule it became theoretically possible for a determined Senator or small group of Senators to prolong debate on a bill by holding forth on the floor of the Senate. The intent of filibuster is to force the majority who had wanted to vote for the bill to withdraw their favored legislation, motivated by exhaustion and disgust. In 1917, under pressure from President Woodrow Wilson, the Senate, disgusted by the blockage of legislation by the filibustering of 12 anti-war Senators adopted a cloture rule. A cloture rule (think "closure") empowers some number of Senators to end a filibuster by voting to cut off debate. In 1917 the number necessary to bring closure to debate was set at 2/3 the number of Senators "present and voting." (Remember the "previous question" rule in the House, essentially a cloture rule that requires only a majority vote to end debate and trigger a vote on "the question," in legislation under consideration.) Since 1917 the U.S. Senate has kept a closture rule but the number of Senators necessary to invoke cloture has been a moving target. In 1975 the Senators themselves voted in a rule that changed the number necessary to invoke cloture. Cloture then required the votes of 3/5 of the Senators "duly chosen and sworn," that is, an absolute number (usually 60)--not just those present at the time. That 1975 rule change is the origin of the current Senate's routine obstructionism based on the modern filibuster.
Americans' concept of the filibuster is shaped by the almost mythological 1939 movie, "Mr. Smith Goes to Washington," starring Jimmy Stewart. (Cathy McMorris Rodger's once declared the film her all time favorite movie.) The high drama of the idealistic Mr. Smith's filibuster wasn't accurate in 1939 and is even less so today. Newly elected Senator Smith's talking filibuster was presented as a wake-up call to a corrupt Senate, rather than the obstructionist tool the talking filibuster was in actual practice.
Today a talking filibuster is a rare piece of drama. Instead, the filibuster in the U.S. Senate has become routinized and almost anonymous. All that a Senator needs to do is have their staff send an email threatening a filibuster. The mere threat effectively blocks legislation from coming to the floor of the Senate for debate, much less an actual vote on the bill's merits. Thus, a Party with 41 votes, without even talking on the floor of the Senate, can obstruct consideration of all legislation it opposes, and the Senate moves on to other business that the Party with the 41 votes deems worthy of consideration. (Originally, the talking filibuster ground the business of the Senate to a halt, preventing it from moving on to consider other business. That obstruction was eliminated in 1970 with adoption of the "two track system." "Under the two-track system, the Senate can have two or more pieces of legislation or nominations pending on the floor simultaneously by designating specific periods during the day when each one will be considered." The two track system avoids the rancor, disgust, and total blockage of Senate business produced by an unpopular filibustering minority Senator. Whether by intent or accident, gradually accreted Senate rules now assure the minority of its ability to obstruct.
This minority obstruction in the Senate is likely a major cause of the public's disapproval of the workings of Congress. Recent surveysshow disapproval as high as 82%. Campaign promises whither and die in the Senate, leaving voters to wonder why they bother to vote.
Senators sometimes acknowledge the legislative constipation induced by the routinized filibuster by changing the rules to allow certain kinds of bills to bypass the artificial need for 60 votes. The five bill categories that bypass the 60 vote threshold are detailed here. The category most used (and lately in the news) is budget reconciliation. Created in 1974 to help keep the government from being shut down by Senate obstructionism, budget reconciliation has more recently become the vehicle of choice for passing legislation through the Senate with only 51 votes. A whole set of additional arcane Senate rules govern the use of budget reconciliation, rules so arcane that the Senate Parliamentarian gets called upon to decide if a proposal fits under the rules. (The parliamentarian recently ruled, for instance, that the $15 federal minimum wage can NOT, under reconciliation rules, be crammed into the Covid Relief bill.) Precisely because budget reconciliation is the only feasible way for legislation to bypass the 60 vote requirement (and because reconciliation can only be used a maximum of three times a year) the reconciliation bill has become the vehicle for the passage of all proposed legislation when the majority party lacks 60 votes (i.e. most of the time). The result is huge, often incomprehensible, unreadable bills that further erode the public's view of Congressional function. Notable recent examples of the use of reconciliation are the failed Republican effort in 2017 (for lack of a majority) to repeal the Affordable Care Act (remember John McCain's famous thumbs-down) and the Republican party line passage the same year of the Tax Cuts and Jobs Act. It is insane that the Senate can pass tax breaks for the wealthy with 51 votes but 60 votes are required to even consider H.R. 1, the For The People Act.
The modern-day Senate filibuster and the twisted lawmaking required to get around it make the Senate, already the most undemocratic institution in our governance, a legislative body subject to the veto power of determined minority that represent a small fraction of the American people. 
The modern filibuster should be voted out of Senate procedure. A simple majority would suffice to do this (the "nuclear option"), a simple majority currently lacking on account of the reluctance of two Senators, Sinema (D-AZ) and Manchin (D-WV). Without jettisoning the filibuster--or at least getting rid of its modern incarnation as a costless email-born objection--Democrats have no chance of enacting most of what they have promised. I fear that if they cannot achieve more of their goals they will pay for it at the ballot box in 2022 on account of further voter disillusionment.
Keep to the high ground,
 The current 50 Republican senators collectively represent 41,549,808 fewer Americans than the 50 Democratic senators (out of a total population of 328,239,523).
P.S. In an impeccably timed new book, “Kill Switch: The Rise of the Modern Senate and The Crippling of American Democracy,” Adam Jentleson lays out the Senate filibuster’s history current use. An interview with Mr. Jentleson entitled “The Racist History Of The Senate Filibuster” on Terry Gross’s Fresh Air is available in your browser or as a podcast. It is a lesson in civics and the anti-democratic nature of our governance. (The discussion of the book starts at 8:17 in the program, if you’re pressed for time. Ezra Klein, writer for the NYTimes, is an eloquent spokesman for putting the filibuster out of its misery. See The Senate Has Become a Dadaist Nightmare from the February 4th, NYTImes. Google "Ezra Klein" for additional interviews. I find his arguments very convincing. His debate opponents fight an uphill, losing battle.
P.P.S. Check out this graphical representation of numbers of Republicans and Democrats in Congress over time:
Note: the graph fails to show the brief 60 vote Senate majority Democrats enjoyed in early 2009 when they passed the Affordable Care Act without the use of reconciliation, the last piece of major legislation passed without bowing to arcane rules made necessary by the use of the reconciliation vehicle.