Senate Judiciary Committee Chairman Sen. Charles E. Grassley (R-Iowa) questions witnesses during a committee hearing entitled 'Whistleblower Retaliation at the FBI: Improving Protections and Oversight' on Capitol Hill on March 4, 2015. (Photo by Drew Angerer/Getty Images)

Lawmakers in states across the country have begun to discuss and, in some cases, take bipartisan action on criminal justice reform.

While some of these efforts have been driven by concerns about racial disparities in sentencing and the long-term effects of mass incarceration, it's the price-tag matters that have helped them pass everywhere from blue states like California and Illinois to Utah, Texas, Mississippi, Alabama, Nebraska and Georgia.

But now it seems that concerns about both the fiscal and social costs of mass incarceration have filtered up to the federal level and made this an increasingly bipartisan -- and thus, potentially successful -- legislative effort.

Here's a look at five major events in 2015 giving champions of sentencing reform new hope that, as Congressional Black Caucus Chairman Rep. Emanuel Cleaver (D-Mo.) told Politico in April, "something is changing." (The caucus has long advocated for such reforms.)

1) Obama made it a priority

In January, President Obama called for criminal justice reforms in his State of the Union address. Obama pointed out that both incarceration and crime rates are falling. Still, the United States continues to far outpace other advanced economies in the share of its population the country imprisons. Events in Ferguson, Mo., Baltimore and other cities have made the need for better policing and increased fairness in the criminal justice system clear, Obama said.

2) Odd couples united for the cause

In February, Roll Call identified a series of what the publication called political "odd couples" -- that is, Republican-Democrat duos who introduced legislation aiming to reduce the share of Americans incarcerated for long periods of time or whose lives are forever changed by such an experience. One bill would require federal prisoners to participate in programs that aim to reduce the prison return rate and reduce the sentences of those who do so.

Another bill would reduce the mandatory minimum sentences that federal judges must currently hand down to people convicted of non-violent drug felonies. It would also address, retroactively, the jail time disparities in sentences given to those caught with crack versus powder cocaine before 2010 -- a frequent talking point of those who argue African Americans receive disparate sentences for similar drug crimes.

And a third bill seeks to restore voting rights to individuals convicted of non-violent felonies after they have completed their sentences.

3) Public officials went on the record

The clamor for criminal justice reform has grown louder on both sides of the aisle, with chastened one-time law-and-order conservatives, those deeply concerned with the cost of the country's elevated incarceration rate and even people vying for the White House willing to weigh in on the issue in very open ways. In April, several presidential candidates, state officials and civil rights activists published essays in a new book featuring their reform ideas, specific concerns about the state of the criminal justice system and incarceration levels.

4) The evidence against mass incarceration mounted

In May, the United States Sentencing Commission released a report identifying a single change in drug-crime sentencing laws that could whittle down the prison terms of about half of all federal inmates and save the country $2.4 billion in incarceration costs alone, according to the Huffington Post.

That study joined others that have found that large numbers of those in prison come from a small set of American communities where the social costs of mass incarceration -- increased poverty and joblessness, poor school performance among the children of inmates as well as increased rates of depression and anxiety -- outstrip the crime-fighting possibilities of the lock-them-up-and-throw-away-the-key philosophy.

5) A key Republican jumped on-board

When that raft of Senate odd-couple legislation was introduced in February, Sen. Charles E. Grassley (R-Iowa) balked. Grassley happens to be the powerful chairman of the Senate Judiciary Committee, the body that most sentencing and criminal justice reform legislation would need to clear in order to face a full vote on the Senate floor. At the time, Grassley described the bills as “lenient and, frankly, dangerous,” according to The New York Times.

But this week, Politico reported that Grassley is now part of a bipartisan group of lawmakers drafting a sentencing reform compromise that would reduce the sentences of well-behaved prisoners and trim down some of the mandatory minimum terms that judges are all but forced to hand down right now.