WASHINGTON — There are few remaining places in modern life where strict decorum is expected as it is in the halls and on the floor of the United States Senate. 

And on Friday, U.S. Sen. Ted Cruz of Texas shattered one of the surest unwritten rules of the upper chamber: He called a colleague a liar.  

It was not just any colleague, for that matter. It was Senate Majority Leader Mitch McConnell. 

"I told my staff, the majority leader looked me in the eye, and looked 54 Republicans in the eye," Cruz, a GOP presidential candidate, said on the Senate floor. "I cannot believe he would tell a flat-out lie." 

The Texas Tribune thanks its sponsors. Become one.

"We now know that when the majority leader looks us in the eyes and makes an explicit commitment, that he is willing to say things that he knows are false." 

Essentially, Cruz accused McConnell, a Kentucky Republican, of misleading Senate Republicans on cutting a deal for the continuation of the Export-Import Bank in order to push for the Trans-Pacific Partnership trade deal. 

The Export-Import Bank is an obscure government agency that is the bane of conservatives. However, business groups and Democrats argue that the bank supports small businesses. 

Its charter expired last month, but it could be resurrected as Congress addresses funding the Highway Trust Fund next week. 

That word, "lie," is one of the most loaded words in American politics. Even in angriest campaign moments, politicians tend to think long and hard before accusing even a despised rival of it. 

Never miss a moment in Texas politics with our daily newsletter.