Washington (CNN) The annual Conservative Political Action Conference is meeting this week in Maryland, and in some ways, it's a good time to be a conservative. Republicans control all branches of the federal government, while Democrats and liberals are shut out.

In other important ways, though, there are signs that conservatism may be peaking, while liberalism is on the rise.

In the early 1970s, the Republican Party was not a conservative one. According to the General Social Survey , only 43% of self-identified Republicans called themselves conservative in 1974. Two years later, Gerald Ford, who 40% of Americans called conservative and 10% of Americans called a liberal in a pre-election CBS News/New York Times poll, beat out the more conservative Ronald Reagan for the Republican presidential nomination.

But when Reagan won the nomination in 1980, the conservative movement was off and running. By the mid-1980s, regularly more than 50% of Republicans called themselves conservatives in General Social Survey data. By the mid-2000s, it was up to 60%.

Republican presidential candidates generally reflected this rise in conservatism. Every Republican nominee from 1980 to 2012 had a wider spread than Ford did in pre-election polling between the percentages of Americans who called the nominee conservative and liberal. This peaked with George W. Bush in 2004, who 68% of Republicans called conservative in a pre-election Gallup survey

This past decade, however, conservatism hasn't been rising. The 64% of Republicans who identified as conservative in the 2016 General Social Survey are not statistically significant different from the 65% who said they were in 2008. In fact, every General Social Survey poll since 2008 has found that conservatives make up about that share of Republicans.

The peaking of conservatism is seen in Gallup's polling as well. Over the course of 2017, 69% of Republicans called themselves conservative. That's up from the 62% of Republicans who said they were conservative in 2001. It's not statistically different from the 70% of Republicans who identified as conservatives at the end of the last decade, however.

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While conservatism growth may have stunted in the Republican electorate, the nominee they chose to lead their party in 2016 was arguably the least conservative in the last 40 years. In Gallup's pre-election poll on the subject, 47% of Americans said Republican Donald Trump was conservative, and 19% called him liberal. The difference between the percentage of Americans who called Trump conservative and liberal -- 28 percentage points -- was the lowest I could find in CBS News/New York Times or Gallup polling for any Republican nominee since at least 1976, when polling on the subject first began.

Trump's nomination came when there were plenty of conservative options. Republican voters passed on Sen. Ted Cruz when the Texan was one of the last candidates standing between Trump and the nomination. Wisconsin Gov. Scott Walker was forced out of the race a few months after entering it

While conservatism may have peaked among Republican, liberalism is clearly on the rise among Democrats. More Democrats (48%) self-identified as liberal in the 2016 General Social Survey than in any other General Social Survey taken since 1974. In Gallup's 2017 data, a record 50% of Democrats said they were liberal. That was a 20 percentage point rise from 2001, when only 30% of Democrats said they were liberal.

The rise of liberalism among Democrats has all but wiped out conservative Democrats. Back in 2001, they made up 25% of Democrats in Gallup polling. That's dropped by nearly half, to only 13% in 2017.

The combination of all these forces led to an all-time high -- since Gallup first tracked it in 1992 -- of 26% of all Americans identifying as liberal in Gallup's polling. An all-time low of 35% of Americans called themselves conservative.

The change in the Democratic electorate has been reflected well in its nominees for president. As an example, look at the difference between Bill and Hillary Clinton. When Bill Clinton first ran for president in 1992, 38% of Americans said he was liberal in a CBS News/New York Times poll and 42% of them said he was liberal in a Gallup survey. In 2016, 58% of Americans said Hillary Clinton was liberal in a Gallup survey.

When you combine CBS News/New York Times data, Hillary Clinton and Barack Obama were the most liberal Democratic nominees for president since at least 1976. And although Trump was seen as the most liberal Republican nominee in at least 40 years, the record for a Democratic nominee being called conservative is still held by Jimmy Carter from 1980 (i.e. the first Democrat in our data set).

As we head into the 2020 campaign, the potential Democratic nominees seem to be falling over each other in trying to move to the left. Sens. Cory Booker of New Jersey, Kirsten Gillibrand of New York and Kamala Harris of California have voted with the President's agenda 15% of the time or less . Gillibrand, who once was a moderate member of Congress from upstate New York, has voted with him a record low 8% of the time.

We'll see if the Democratic electorate responds to this liberalism. As Trump showed, sometimes an ideologically polarized electorate makes a surprising choice.