WASHINGTON – His delegate lead growing, Mitt Romney gently nudged his Republican opponents toward the sidelines on Wednesday and said he was on track to wrap up the presidential nomination before the party convention next summer. Rick Santorum and Newt Gingrich paid him no mind, vowing to fight on in a campaign marked by persistent ideological divisions.

If anything, the political maneuvering intensified as the marathon pointed toward contests in five states over the next week. Romney’s campaign purchased television advertising time in Alabama according to campaign sources, as it pursued a breakthrough in the party’s Southern base.

A Santorum ally urged Gingrich to abandon the race.

In response, the former House speaker said he would consider it — if he thought Santorum was sure to beat Romney and then President Obama. “I don’t,” he added.

One day after Super Tuesday, Romney’s campaign circulated a memo making the case that his six victories on a single night had increased his delegate lead to a point that it was increasingly hard for any of his rivals to catch up. And they were hurting the party by continuing to try, it suggested.

“As Governor Romney’s opponents attempt to ignore the basic principles of math, the only person’s odds of winning they are increasing are President Barack Obama’s,” it said.

Romney didn’t go that far in an interview, and he stopped short of a flat prediction that he would achieve his goal of a pre-convention delegate majority. “We think that will get done before the convention, but one thing I can tell you for sure is there’s not going to be some brokered convention where some new person comes in and becomes the nominee,” he said on CNBC’s “Squawk Box.” “It’s going to be one of the four people that are still running.”

After Super Tuesday, Romney has 419 delegates overall, more than his three rivals combined. Santorum is second with 178; Gingrich has 107; and Paul has 47. It takes 1,144 to win the nomination.

While Romney clearly would like all his opponents to drop out, the departure of just one — either Santorum or Gingrich — might be less welcome. The two often divide the anti-Romney vote and enable him to win contests he might otherwise lose. In Ohio on Tuesday, Romney edged Santorum by a little more than 10,000 votes out of 1.2 million cast. Gingrich drew about 175,000 votes, and Ron Paul 111,000.

Gingrich and Santorum both argue that despite Romney’s financial and organization advantages, he is a latecomer to conservative causes, plagued by inconsistencies in his record and unable to articulate significant differences with Obama.

Earlier this week, Romney abruptly abandoned a position he has held since he ran for governor to link increases in the federal minimum wage to rises in inflation. He had reaffirmed it as recently as last month, telling reporters aboard his campaign jet, “I haven’t changed my thoughts on that.” But Santorum and Gingrich hold opposing views, as do Republican business allies, and on Tuesday, Romney said on CNBC, “There’s probably not a need to raise the minimum wage.”

In a post-Super Tuesday interview, Romney also said there is no current way of proving that his proposed tax cuts wouldn’t raise the deficits, “because those kind of details have to be worked out with Congress and we have a wide array of options.”

He has called for a 20 percent reduction across the board in personal income tax rates and says he will recommend curbing some of the existing tax breaks that wealthier taxpayers currently enjoy. Asked what level of income would qualify as wealthy, he sidestepped.

“What I’ll look at is the various cohorts, the top 5 percent, the top 10 percent, the top 25 percent, we’ll look across the code at the various categories and see if they’re continuing to pay the approximate share that they’ve paid in the past under the current system,” he said.

“It’s important that the great majority of Americans don’t see an increase in their tax share,” he added.

Romney spent the day in Massachusetts after sleeping at home for the first time in weeks, a result of a nominating campaign that has gone on longer than any in recent years.

Santorum campaigned in Kansas, which holds caucuses next Saturday with 40 delegates at stake. Wyoming, with 12 delegates, is also on the calendar, as are the Virgin Islands, Guam and the Northern Marianna Islands, with six apiece.