Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE built a multi-billion-dollar real estate empire, became a national celebrity, and then won the White House. But, does he know that 52, minus three, equals 49? One wonders.

There are 52 Republican senators. If a vote in the Senate is tied 50 to 50, Vice President Mike Pence Michael (Mike) Richard PenceGardner signals support for taking up Supreme Court nominee this year Biden leads Trump by 12 points among Catholic voters: poll GOP brushes back charges of hypocrisy in Supreme Court fight MORE is entitled to vote to break the tie. But, if three Republicans defect in a 49 to 51 vote, there is no tie, the vice president does not get a vote, and a bill supported by 49 Republicans is defeated.

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This is simple arithmetic — but it is apparently still not fully grasped by the current occupant of the Oval Office.

In both the primary and general election, Trump used social media to attack his opponents with a degree of ferocity that was perhaps unprecedented in modern-day politics. And, whether that tactic hindered or helped, we know he succeeded in winning the presidency.

Based on that startling success, Trump apparently has concluded that, even as president, it never hurts to indulge what is perhaps his natural instinct to savage anyone who might be deemed an adversary or even merely a critic of him or his administration. That conclusion is profoundly mistaken. Such attacks do hurt — and the person they hurt most is Trump.

During the primary campaign, Trump denigrated Sen. John McCain's (R-Ariz.) experience as a prisoner of war in Vietnam. It is not clear why he chose to attack McCain, who was not even a candidate. But, even after the election and McCain’s subsequent struggle with brain cancer, the two men have continued to trade insults. Trump, who could afford to be gracious after his electoral victory, has made no apparent effort to bridge the gap.

It was, of course, McCain who cast the deciding 51st vote against the so-called “skinny” bill that would have repealed ObamaCare. Passage of that legislation would have been a very substantial victory for a Republican president who campaigned on a promise to repeal and replace ObamaCare.

I do not know whether personal animosity between Trump and McCain affected the senator’s negative vote. But, one does not have to be a student of Freudian theory to appreciate a simple human truth: Our personal feelings can and often do affect the decisions we make in our professional lives. Trump’s attacks certainly did not increase the likelihood that McCain would support legislation favored by Trump.

The Republicans have, at least for the time being, given up on repeal-and-replace and turned instead to tax reform. And now the whole world watches while Trump trades barbs with two other Republican senators: Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump MORE (R-Tenn.) and Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (R-Ariz.). Both senators have terms that end in January of 2019, and both have announced that they will not run for reelection in 2018.

Not running for reelection seems to have liberated both senators to express more freely than they might otherwise their dissatisfaction with Trump’s performance in office. Corker famously likened the White House to an adult day care center, and he warned that Trump might lead the U.S. into World War III. Trump responded that Corker could not be elected dogcatcher in Tennessee.

Flake asserted, "It is … clear to me for the moment we have given in or given up on [Republican] core principles in favor of the more viscerally satisfying anger and resentment." Although he never uttered the president’s name, no one doubted the target of Flake’s criticism. Trump then mocked Flake’s low approval rating and boasted of the standing ovations he had received from the Republican senatorial caucus. My guess is that McCain, Corker and Flake did not join in those ovations.

It is of no importance who “started” these feuds between Republican senators and Trump; childish disputes about who started a fight are beneath the dignity of senators and the president. What should be of primary importance, particularly to a president whose term most definitely will not end in 2019, is successfully enacting significant tax reform, which all Republicans purportedly favor.

If Republicans are to enact significant tax reform before the 2018 mid-term elections, they cannot afford to lose more than two votes on a straight party-line vote. It is possible of course that some Democratic senators might vote for the Republican tax reform proposal, but no prudent person — and no prudent Republican president — would assume that will happen.

Republicans will have to thread a needle with a very narrow eye to enact tax reform. They failed to accomplish that task with regard to repealing and replacing ObamaCare. Tax reform will not become any easier if Trump continues to trade insults with Corker and Flake.

I began by asking whether Trump knows that 52, minus three, equals 49. Here’s another math teaser for the president: How many months are there between now and January of 2019?