A frequent accusation that has been leveled at Republican politicians is that they did nothing to fight the Obama agenda, even though they had a majority in both houses of Congress. Supposedly the rank and file now see them as useless or unprincipled, and so are going with Donald Trump, or possibly Ted Cruz.

One reason for inaction is that when the Republicans did take a stand, in 2013, under the initiative of Ted Cruz and others, the public blamed them for the results. A confrontation with Obama led to a partial shutdown of the government. Polls showed Republicans were blamed by 53% of the public. This echoed the experience of 1995, when led by Newt Gingrich the Republicans shut down President Clinton's government to halt excessive spending. Gingrich felt the brunt of the blame then also.

The resulting cautious thinking was demonstrated by Republican Lindsey Graham who said in 2015: "...You want to lose in 2016? Let it be seen that the Republicans in the House and Senate can't govern, then that's the end of our 2016 hopes."

In his book A Time for Truth, Ted Cruz describes the events in 2013 that led to the shutdown. He says that he and Senator Mike Lee had asked their Republican colleagues "What are you going to do to stop Obamacare from kicking in?" and the answer was always nothing, since a fight was risky, and could imperil re-election. Cruz 's idea was that Congress should fund everything except for ObamaCare. This is within the power of Congress, and is known as "the power of the purse."  The big obstacle was Obama's veto power, but Cruz hoped that if he got enough Republicans, plus Democrats from "red" (conservative) states, he might put enough pressure on Obama to reach some sort of compromise.  Ted's colleagues responded "Absolutely not!" and advised "Wait until the debt ceiling", which did come along, but they did nothing then either. 

Cruz and Lee traveled the country to get support, and more than two million Americans signed a petition to stop ObamaCare, and also phoned Capitol Hill. The Senate Republican leadership directed their fire -- not at ObamaCare, but at Cruz. Twenty senators went on every TV channel, and "carpet-bombed" the House Republicans for the initiative. 

Cruz emphasized that he did not shut down the government. Obama did. "After every vote to fund the government, Harry Reid and the Senate Democrats said: We don't like your legislation; therefore we're going to shut down the government. "Thus, every time the House voted to fund the government, Senate Democrats voted it down on a party-line vote, and the media dutifully repeated that it was Republicans who had shut down the government." 

When the shutdown was over, high-ranking Republican party members were angry that colleagues forcing a shutdown had backed them into a corner and left them shouldering much of the blame for an initiative that they claimed had no chance of succeeding.

In practice, this meant that after 2013 they gave up the "power of the purse" which meant that Democratic initiatives were often impossible to oppose.

This does seem to show that there is a valid complaint against part of "the establishment". The establishment is risk-averse. Another example of this was when John McCain ran for president, with Sarah Palin his candidate for vice president. She said this:

I was banned from talking about Jeremiah Wright and Obama's friend, Bill Ayers, the character that he befriended and kicked off his political campaign in the guy's living room," Palin said. "Couldn't talk about that."

Palin pointed a finger at who she thought was to blame.

I was not allowed to talk about things like that because those elitists, those who are the brainiacs in the GOP machine running John McCain's campaign at the time, said that the media would eat us alive if we brought up these things.

Bill Ayers, in his radical youth, bombed the Pentagon, and Jeremiah Wright (Obama's pastor) said that the disaster of 9/11 was "America's chickens, coming home to roost."

In retrospect, taking a risk would have made sense, since despite all the Republican caution, Obama won.

We can see that Republicans did make some effort to rein in the Democrats, by looking at bills they submitted that Obama vetoed or threated to veto.

Obama vetoed a bill to allow the Keystone pipeline to be built. This pipeline would have carried oil from Canada to the refineries in the south.  He also vetoed a bill to defund Planned Parenthood and Obamacare. He vetoed two resolutions that attempted to stop the EPA's "Carbon Pollution" regulations. He vetoed other legislation as well.

He threatened to veto a bill to apply sanctions to Iran, as well as The Regulatory Accountability Act of 2015 (HR 185) and the Promoting Job Creation and Reducing Small Business Burdens Act (HR 37). HR 37 would have repealed "Dodd Frank Wall Street Reform Act", a counterproductive bill that was partly written by Barney Frank, who himself refused to reform Fannie Mae and Freddie Mac, which led to the housing implosion that the bill was supposedly going to solve.

So while there were efforts to stop Obama, they didn't get far.  And unfortunately, much of the damage done by the Obama administration is done by executive agencies such as the EPA, or the IRS, or the FCC, damage which the Congress cannot reverse. 

There is another accusation, which is that the Republicans, on some issues, did not even disagree with the Democrat's agenda.

For instance, Michelle Malkin gave a fiery speech at CPAC, where she said:

I am telling you the truth, I am asking you to do your homework, I’m asking you to follow the money. I know it’s what you don’t want to hear, but do you want to hear the same Republicans promise you, as they had been since 1981, that they’re going to abolish the Federal Department of Education? It’s an empty talking point, and those empty talking points need to be punctured like helium balloons.

In an article on the disconnect between the Republican establishment and the public by Victor Davis Hanson, he gives an example:

The children of Republican elites do not sit in classes where a quarter of the students do not speak English...Their children are not on buses where an altercation between squabbling eight year olds leads to a tattooed parent arriving at your home to challenge you to a fight over “disrespecting” his family name. The establishment Republicans have rarely jogged around their neighborhoods only to be attacked by pit bulls, whose owners have little desire to speak English, much less to cage, vaccinate, or license their dogs.

So to sum up, if you are a Republican politician who feels ambushed by the successes of Donald Trump, you should realize that if people feel you are either unable or unwilling to stand up to the leftist agenda, or if you don't understand their problems, they may see you as a liar, or a pushover, and look for alternatives.