President Trump has changed the Republican Party and what it stands for. But after losing the House of Representatives to the Democrats in the Nov. 6 midterm elections, Republicans need to ask themselves: Is the way President Trump governs sustainable? Or, will it will lead to further election losses in 2020 – including for Trump himself?

After Mitt Romney was defeated by President Obama in the 2012 presidential election, the Republican National Committee asked me and several other Republicans to study what went wrong. One of our recommendations was for the party to become more inclusive in an increasingly diverse nation.

President Trump has expanded the party by gaining support from many formerly Democratic blue-collar voters without college degrees. But along the way, he lost many previously Republican college-educated voters – particularly women, who voted 59 percent to 40 percent for the Democrats the midterm elections.

Historically, the impact presidents have on political parties is short-term. For example, are the Democrats the party of Presidents Bill Clinton or Barack Obama right now? Are Republicans the party of President George W. Bush?

Demographic changes, however, are long-term. And the demographics of America are trending away from Republicans, as we predicted in the post-Romney report. That’s because America is becoming more diverse – meaning less white.

In the 2006 midterm elections, 79 percent of voters were white. In last month’s midterms, the share of white voters dropped to 72 percent. They favored Republicans by 4 points.

The shrinking white voter trend is also true in presidential election years. When George W. Bush was elected president in 2000, 81 percent of voters were white. In contrast, when Trump was elected president in 2016, only 71 percent of voters were white – a 10-point drop.

In 2000, white voters preferred Bush to then-Vice President Al Gore by 13 points. Trump won white voters by 20 points.

By 2020, America will be even less white. That means that unless the GOP does better with black and Hispanic voters, the only way the party of Lincoln can win would be to gain an even larger share of a smaller white voting bloc.

Can Trump do it again? Maybe. But even if he can, where does that leave the rest of the GOP? And what will the Republican Party do – and stand for – in either two or six years, when Trump is out office?

If President Trump’s re-election campaign is based on running only to appeal to his base, the GOP will be taking a giant risk. Trump’s base is loyal – but narrow.

If the GOP is proud of its policies, it should seek support for them from all people, regardless of race or gender. Good ideas attract voters, but Republicans have struggled to gain the support of minorities and women for too long.

Both Trump and Romney won white voters by 20 points. Trump lost black and Hispanic voters in 2016 by a smaller margin than Romney did four years earlier, when Romney ran against America’s first black president.

But contrary to conventional wisdom, Trump’s margin of victory was supplied by Hispanic and African-American voters.

In 2012, Romney lost the Hispanic vote by 44 points. Trump lost Hispanics by smaller margin of 38 points.

Romney lost the African-American vote by 87 points. Trump lost the black vote by 81 points in 2016 – a smaller margin, but still a huge gap.

If President Trump’s re-election campaign is based on running only to appeal to his base, the GOP will be taking a giant risk. Trump’s base is loyal – but narrow. In a presidential year, the winner is typically the candidate who can keep his base and pick up just enough voters in the middle to go over the top.

The president and Republicans need to expand their appeal. They must remember there are millions of voters who don’t consider themselves Trump loyalists, but who would be inclined to vote for the president’s re-election – and for other GOP candidates – if the message Republicans communicate appeals to them.

With the strong economy and the low unemployment rates among African-Americans and Hispanics that our country enjoys today, President Trump can expand his appeal if he makes that a priority. But if people think the president doesn’t really care about them, they won’t be inclined to vote for him – even if their personal economic circumstances are improved.

If the president’s message is truculent and it comes across as not caring about those who don’t attend his rallies or are already strong supporters, it will be hard to expand the base.

President Trump needs to be more inclusive.

As president-elect, Trump told Leslie Stahl of “60 Minutes” that he was “saddened” by instances in which some of his supporters engaged in racial slurs against African-Americans, Hispanics and gays. He looked directly into the camera and said “stop it,” as he promised to bring the country together.

President-elect Trump’s message was the right one. President Trump needs to return to it.

The GOP needs to pass criminal justice reform and immigration reform. Educational choice and opportunity must remain priorities. When racist incidents take place, the president should speak out against them. His tone is important. He sets an example and it should be a welcoming, inclusive one.

This year’s midterms should be a lesson for the president. The economy is booming, yet he did not get credit. His job approval in polls is in the low 40s – a low mark in a high-performing economy.

But the president is stuck in the low 40s because that’s about the size of his base. To win, he needs more than just the base.

Hillary Clinton won almost 3 million more popular votes than Trump, who captured only about 46 percent of the popular vote. The only reason Trump is president today is because he won in the Electoral College.

The best way for President Trump to improve his job approval – and therefore the likelihood of his re-election – is to speak and act as president of all Americans, not just his base.