Republican presidential candidate U.S. Senator Rand Paul (R-KY) speaks at the First in the Nation Republican Leadership Conference in Nashua, New Hampshire April 18, 2015. Reuters Rand Paul took a left turn on his journey to the Republican nomination, and now his hopes seem to be headed south.

The libertarian Kentucky senator's new book, "Taking a Stand," came out Tuesday, and it is chock-full of lines that would position Paul well — if he were running against Hillary Clinton for the Democratic nomination.

On the environment: "You'll find I'm a tree hugger, literally . . . I'm a Republican who wants clean air, clean water, and the life-extending miracle of electricity. I compost."

On Wall Street: "Only in a world of crony capitalism would bankers whose faulty decisions caused bankruptcy be allowed to cash out as the middle class absorbs the losses."

On his party: "Right now, the Republican brand sucks. I promised Reince Priebus, the chairman of the Republican National Committee, that I would stop saying the GOP sucks, and I will (except for this last time)."

On racial minorities: "I want a New GOP that resonates with America, that looks like America — white and black. . . . The face of the Republican Party should not be about suppressing the vote but about enhancing the vote."

On Ferguson, Mo.: "[T]housands of peaceful protesters were met with rubber bullets, tear gas, and a police department that showed up at the protest in gear more fitting for Fallujah or Kandahar."

On drug sentencing: "We should free those who are in jail under the old guidelines. Our prisons are bursting with young men — and women — who are poor or of color."

But Paul has a problem: He isn't running for the Democratic nomination. And though Paul may think his Republican Party's brand sucks, the primary voters don't necessarily share his view that the party is too old and too white. His candidacy has so far failed to ignite — and, indeed, he seems to be fading as a force within the party.

Rand Paul. Scott Olson/Getty Images The most recent national poll, by Fox News, has Paul in sixth place, with 7 percent, trailing Jeb Bush, Ben Carson, Scott Walker, Mike Huckabee and Marco Rubio. Paul averages only about half the support he had late in 2013. Paul doesn't appear to be winning over young voters — perhaps the most important justification for his candidacy — and does not do better than other Republicans, according to a survey released last month by Harvard University's Institute of Politics. Even in his home state, a media consortium poll this month found that Paul had lost his lead in a theoretical matchup with Clinton.

Paul's declining standing can be felt in Washington. Last week, he attempted to reprise his wildly successful 2013 filibuster, which caught fire on social media and forced party leaders to take notice. But this time Paul found indifference as he fought to limit government surveillance. As The Post's Philip Bump reported, it got only about one-tenth of the Twitter attention that his first effort did. Television footage from the chamber caught Sen. Lindsey Graham (R-S.C.) rolling his eyes as Paul spoke last week, and Senate GOP leader Mitch McConnell (Ky.), who joined Paul's previous filibuster, openly opposed him this time.

Sen. Rand Paul (R-Kentucky) on the "Today" show. 'Today' On CBS's morning show Tuesday, Paul was asked to answer his Republican colleagues' complaint that his 11-hour speech was really a performance aimed at selling his new book; "Fox & Friends" minutes later asked him to respond to the charge that he is a "misguided ideologue."

"Rand Paul has now decided he wants to be a liberal Democrat," conservative commentator William Kristol said Sunday on ABC's "This Week."

Paul is no liberal; his new book repeats all his conservative ideas about ending Obamacare, slashing government spending, auditing the Fed and privatizing Medicare, and he has the requisite references to free-market economists Ludwig von Mises and Friedrich Hayek.

But Paul is clearly separating himself from the rest of the GOP, both in his new book (in which he cites Pink Floyd, mentions that he met his wife over a beer keg and quotes Martin Luther King Jr. liberally) and in recent remarks. (He told an audience last week that he "didn't run for office" because of the abortion issue.)

At least rhetorically, he is trying to get "rid of the old crust in the Republican Party," by declaring that the Bill of Rights protections are "especially for minorities," that Democrats are not "the only ones allowed to like the environment" and that gerrymandered districts must be undone.

Paul is outraged that "the connected rich didn't get a scratch" when Wall Street collapsed. "They convinced Congress to have the middle-class taxpayer bail them out and went on as if nothing had happened. It's infuriating."

It is infuriating. What's probably more infuriating to Paul is so few in his party share his indignation.