After the plan to repeal and replace the Affordable Care Act failed in the Senate, President Trump began tweeting about changing the rules in the Senate.

"If Republicans are going to pass great future legislation in the Senate, they must immediately go to a 51 vote majority, not senseless 60...," he tweeted.

If Republicans are going to pass great future legislation in the Senate, they must immediately go to a 51 vote majority, not senseless 60... — Donald J. Trump (@realDonaldTrump) July 28, 2017

In most cases, legislation requires 60 votes in the Senate for passage, although this was not the case in the vote on the so-called "skinny repeal" early Friday morning. That amendment was, in fact, one that required only a simple majority of 51 senators to pass. GOP Senators Susan Collins, John McCain and Lisa Murkowski voted no, leaving Republicans short one vote.

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Mr. Trump then tweeted again, adding, "Even though parts of healthcare could pass at 51, some really good things need 60. So many great future bills & budgets need 60 votes."

...Even though parts of healthcare could pass at 51, some really good things need 60. So many great future bills & budgets need 60 votes.... — Donald J. Trump (@realDonaldTrump) July 28, 2017

Over the past few days, the Senate parliamentarian provided guidance that parts of the Senate plan to repeal Obamacare would require 60 votes, rather than 51, because they did not comply with what's known as the "Byrd Rule." This is the rule that bans the Senate from considering "extraneous matter" as part of a reconciliation bill. The Senate was using the budgetary tool of reconciliation to try to pass its health care bill with just 51 votes.

Amendments are considered "extraneous" by the parliamentarian if, for example, they don't produce a change in outlays or revenues, or if those changes are just incidental to the components of the provision that don't relate to the budget.

Immediately after the measure failed, the president tweeted that the three Republicans and 48 Democrats had "let the American people down," and "As I said from the beginning, let ObamaCare implode, then deal. Watch!"

Congress has not yet determined what its next steps on health care will be.