DENVER — Three-fourths of Americans say it’s inevitable that marijuana will be legal for recreational use across the nation, whether they support such policies or not, according to a public opinion poll released Wednesday that highlights shifting in attitudes following an era of drug war and “tough on crime” legislation.The Pew Research Center survey also shows increased support for ending mandatory minimum prison sentences for non-violent drug offenders and doing away altogether with jail time for small amounts of marijuana. The opinions come as public debate on these topics has led lawmakers around the nation to consider policy changes. Since California became the first state to legalize medical marijuana in 1996, at least 19 others, and the District of Columbia, have followed suit, including two that have approved recreational use. More than a dozen state legislatures considered legalization measures this year. Meanwhile, critics and political leaders, both liberal and conservative, have clamored for an end to harsh drug sentences, saying mandatory minimums have contributed to prison overcrowding, civil rights violations and strained budgets. U.S. Attorney General Eric Holder has been pushing Congress to overhaul drug sentencing policies. The telephone survey found that 75 percent of respondents — including majorities of both supporters and opponents of legal marijuana– think that the sale and use of pot eventually will be legal nationwide.