WASHINGTON – Gun control is back as a Democratic campaign issue.

When President Obama said Tuesday that he'll bypass Congress to force more background checks on gun purchases, Hillary Clinton, the leading Democrat running to replace him, thanked him on Twitter for taking "a crucial step" against gun violence and concluded that "our next president has to build on that progress — not rip it away."

Clinton rival Bernie Sanders, who as a U.S. senator representing rural Vermont holds a more mixed record on gun control, said he, too, is with Obama because of the "moral outrage" of so many mass shootings in recent years.

For more than two decades, Democrats have been spooked about campaigning aggressively for gun control, after voter backlash to gun limits and the rising political power of the National Rifle Association were seen as factors in Democrats losing Congress in 1994 and the White House in 2000. Going after guns didn't fit with Democrats' efforts to win back more centrist voters in rural parts of the country.

If the current dynamic holds, this year may be different. "It now will be more of an issue than we've seen in the last two presidential election cycles," said Robert J. Spitzer, author of five books on gun policy and chairman of the political science department at the State University of New York at Cortland.

Even as Republican presidential hopefuls railed Tuesday against Obama's moves, a confluence of factors appears to be making it safer and in some cases smarter for Democrats to openly embrace gun control. They include high-profile mass shootings over the past five years.

Obama's second-term focus on gun violence and his decision to emphasize possible solutions that have broad public support, such as background checks, rather than controversial policies, such as bans, kept the issue in the spotlight.

The increased focus on guns takes some of its cues from changing U.S. demographics, and helps explain why Democrats are giving voice to the issue. White men 55 and older are the most likely group in the U.S. to own guns, for example, while women and minority voters comprising increasing proportions of Democrats and the overall electorate.

"Hillary really was the first to step in this direction and she did it in part … to outflank Bernie Sanders on the left," Spitzer said of embracing gun control. "There is a sense that the gun issue is still complicated but it's a good issue to rally the Democratic base. There's still some wariness … to be sure, but the idea of the gun issue as taboo is, I think, by the boards."