For most of his time in the White House, congressional Republicans have behaved as though Donald Trump was holding their children hostage in a White House dungeon. They’ve been eager to please, quick to excuse and deathly afraid to challenge. They’ve been distinguishable from sheep only because sheep don’t volunteer to be shorn.

But lately, some in the flock have been baring their teeth. Being humiliated, ignored and taken for granted by an overbearing narcissist who has little regard for conservative principles has lost its charm for a group of Republican lawmakers. They have begun to act on the novel idea that they have every right to oppose a president of their own party when he’s wrong.

We got inklings last year. Following the murder of U.S. resident Jamal Khashoggi by Saudi Arabian agents, President Trump allowed no daylight between him and Saudi Crown Prince Mohammed bin Salman, who is believed to have ordered the killing. Secretary of State Mike Pompeo sneered that the objections were mere “caterwauling” from the “salons of Washington.” On a visit to Riyadh, Trump did everything short of picking up the prince’s dry cleaning to show that nothing had changed.

The brown-nosing was too much for many lawmakers to bear. In December, the Republican-controlled Senate approved a resolution stipulating that “Crown Prince Mohammed bin Salman is responsible for the murder of Jamal Khashoggi” and demanding that the Saudi government “ensure appropriate accountability for all those responsible for Jamal Khashoggi’s murder.”

On Wednesday, Trump got another fastball under his chin. The Senate voted to cut off American military aid to the Saudi war effort in Yemen — which has produced what the United Nations ranks as the worst humanitarian crisis on Earth. Sen. Mike Lee of Utah was one of the Republicans urging his colleagues to “end our involvement in this unauthorized, unjustified and immoral war.” Seven GOP members chose to break with the administration.

The House must approve the measure, and if it does, Trump will have to decide whether to exercise his veto for the first time. He used it Friday on one, passed by the Senate Thursday, that invalidated the national emergency he declared in February in order to filch funds to build his border wall.

He had resorted to this ploy because of yet another show of defiance on Capitol Hill. Unable to strong-arm Congress to grant him $5.7 billion for this harebrained project, he put the country through a pointless 35-day government shutdown before finally signing a short-term funding bill. When lawmakers passed a longer-term funding bill, they again omitted his favorite fantasy. He signed that bill as well — and then resorted to the bogus decree to redirect money Congress had provided for other purposes.

Presidential emergency declarations have become a regular feature of our dysfunctional government. Trump, however, upped the ante, using it to get something Congress had refused him even when the GOP controlled both houses. Democrats denounced his declaration as an outrageous expansion of presidential power — and chortled that a Democratic president could someday make use of this option for grand progressive purposes. On Thursday, a dozen GOP senators joined them in telling Trump where he could put his emergency.

This sort of independence should not be the rare exception. The framers of the Constitution took it for granted that Congress would stoutly resist efforts by the president to expand his role. In The Federalist Papers, James Madison wrote, “In republican government, the legislative authority necessarily predominates.” He actually worried about “the weakness of the executive” in the face of an overly powerful Congress.

His fears were misplaced. In recent practice, party loyalty has often disabled the checks and balances in the Constitution. Members of both parties have often found it congenial to surrender control to the president.

On Wednesday, Sen. Bernie Sanders (I-VT), said the Yemen vote means that “Congress is going to reassert its constitutional responsibility over issues of war that have been abdicated.” That greatly overstates the case, considering that Congress has not acted to end military operations in Afghanistan, Syria, Somalia, Libya or Niger.

Steve Chapman blogs at http://www.chicagotribune.com/news/opinion/chapman. Follow him on Twitter @SteveChapman13 or at https://www.facebook.com/stevechapman13. To find out more about Steve Chapman and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.